Two major mysteries in science, the nature of dark matter and the possible existence of higher dimensions, could be linked, new research suggests. The team behind a new study proposes that dark matter may be so strange and ghost-like because it is in tune with a fifth dimension.

When scientists discuss "extra dimensions," they aren't talking about other universes in which another evil version of you exists (and with a beard). Instead, they refer to dimensions that could be "curled up" with reality alongside the standard four-dimensional spacetime, consisting of the three dimensions of space and one dimension of time.

While these extra dimensions remain highly speculative, they have become a hot topic, especially as string theory, the most popular extension to standard physics, relies upon the existence of at least 11 dimensions. Scientists are more sure that dark matter exists, but proving its existence still remains troubling because, despite its gravity literally holding galaxies together and outweighing ordinary matter by around five to one, it remains effectively invisible because it doesn't interact with light and it simply ghosts through ordinary matter.

"Understanding dark matter would represent a profound advance in humanity's knowledge of the cosmos and what it is made of," team member Yu-Dai Tsai of the University of Sheffield said in a statement.

"Our research gives physicists clear new targets in the search for dark matter, while connecting two of the biggest ideas in fundamental physics: the mystery of dark matter and the existence of hidden dimensions."

Dark photons play dark matter like a violin

Though the main idea is that dark matter may operate in the fifth dimension, this new research expands upon that concept with another theory. It suggests that dark matter exists with another inhabitant of the fifth dimension, a force-carrying particle called a "dark photon."

Standard photons are the constituent particles of electromagnetic radiation, or light; dark photons would be similar but for a hypothetical "dark force."

The team's new proposal would see the unique geometry of the fifth dimension causing the masses of dark matter particles to form an arrangement that gives rise to a "dark matter resonance." This is akin to the intense vibration of a musical instrument at certain notes.

"Dark matter resonance is already known to be a powerful idea, with the potential to change our understanding of how dark matter was produced in the early universe and how we search for it today," team member Yu-Dai Tsai of the University of Sheffield said in a statement. "But many previous resonant dark matter models have treated the resonance as an assumption. This work gives a possible deeper origin for it: the resonance may come directly from the geometry of hidden dimensions."

Tsai explained that while dark matter resonance is a phenomenon that has been explored before, the research conducted by this team differs because it suggests dark matter resonance is not a coincidence. Instead, the possible deeper origin for the resonance sees it emerge directly from the geometry of hidden dimensions. This would allow dark matter to interact strongly shortly after the Big Bang while allowing it to settle into its ghost-like inert existence today.

"This resonance can make dark matter interactions much stronger at crucial epochs in cosmic history, such as in the early universe," Tsai added. "Crucially, the model allows for these strong interactions in the past while still explaining why dark matter appears so inert and hard to detect today."

Of course, it is very early days for the team's theory, but it excitingly offers a way toward solving two of the universe's greatest mysteries.

The team's research was published in the Physical Review D.

On July 4, the United States of America celebrates its 250th birthday, marking the anniversary of the Declaration of Independence and becoming a sovereign nation.

Today, this relatively young country leads the way in our understanding of the universe. It's where many major players in space science, like NASA, the California Institute of Technology (Caltech), the Massachusetts Institute of Technology (MIT), and Northwestern University, to name just a few.

And to celebrate 250 years of the U.S. as an independent nation, Space.com takes you on a journey through some common misunderstandings of the universe through the years and the roles American scientists played in clearing up that cosmic confusion.

By 1776, Sir Isaac Newton's laws of motion had been around for about 89 years since the publication of Philosophiæ Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy) in 1687. Five of the solar system planets had been discovered by the Ancient Greeks long before the birth of the U.S. Also, after a long struggle and many attempts to stifle this knowledge, humans were made aware that the Earth orbits the sun rather than the other way around, with the final nail in this coffin of misunderstanding laid by Polish astronomer Nicolaus Copernicus in 1543 and Galileo Galilei in 1610, receiving an extra hammer blow from Newton in 1687.

Galileo had also delivered us to the understanding that not only was Earth's place in the solar system unique, but it wasn't even the only planet to possess moons, with the moons of Jupiter, Io, Europa, Ganymede and Callisto discovered in 1610.

Clearly, by the time the U.S. was born we were already beginning to understand the universe and our place within it, but some major misunderstandings still persisted. One of the largest of these surrounded the nature of the sun itself.

The sun as a burning lump of coal

America was formed during the "steam age," a period of industrialization that lasted from 1770 to 1914. This revolution was driven by coal, powering locomotives, ships, and factories, changing the shape of industry, transportation, and manufacturing. At this time, coal was the densest and most powerful fuel source known to humanity, so it is perhaps little wonder that many early scientists theorized the sun was actually a tremendously massive lump of burning coal.

Then, one of the oldest and most prominent scientific periodicals in the world, the U.S.-based Scientific American, wrote a 1863 article that first began the pushback against the sun as a burning lump of coal.

"If the sun were composed of coal, it would last at the present rate only 5,000 years. The sun, in all probability, is not a burning, but an incandescent, body. Its light is rather that of a glowing molten metal than that of a burning furnace. But it is impossible that the sun should constantly be giving out heat, without either losing heat or being supplied with new fuel," the Scientific American article stated. "Assuming that the heat of the sun has been kept up by meteoric bodies falling into it, it is possible from the mass of the solar system to determine approximately the period during which the sun has shone. The limits lie between 100 millions and 400 millions of years."

Though this estimate was still miles out, we now understand that the sun is around 4.6 billion years old; this development came at a time of a geological revolution that was uncovering evidence that our planet was much older than theological estimates of just a few thousand years.

Around 57 years later in 1920, British scientist Arthur Eddington first suggested stars like the sun are actually powered by the nuclear fusion of hydrogen to helium. The idea was published by Eddington in his 1926 book, "The Internal Constitution of the Stars." Twelve years after this, nuclear physicist Hans Bethe formulated the first explanation of this nuclear fusion process, detailing the proton-proton chain reaction and the Carbon-Nitrogen-Oxygen (CNO) cycle.

The idea of the sun as a burning lump of coal finally burnt out 162 years after the formation of the U.S., a chain reaction kick-started by an American publication.

Ether or…?

During the infancy of the U.S. in the 1800s, scientists understood that light is a wave. Applying this to what they knew of other waves, it was logical to presume that light also needed a medium through which it could propagate. This medium would have to be ubiquitous and possess some unique properties to allow light to propagate through it at the speed of light.

Thus, it was proposed that space was filled with a medium called the luminiferous ether, with luminiferous meaning "light-bearing." The fact that this would have to be an invisible and infinite material that doesn't interact with physical objects made the existence of the luminiferous ether highly controversial.

We now know this medium doesn't exist, and that is thanks to two American physicists, Albert A. Michelson and Edward W. Morley, who in 1887 delivered the most important null result in the history of science: disproving the existence of the luminiferous ether.

Should the luminiferous ether exist, then scientists reasoned that as the Earth orbits the sun at around 66,000 miles per hour (106,216 kilometers per hour), our planet should be moving through the ether, which had been deemed to be stationary. That meant Earth must be moving with respect to the stationary ether. And if the ether is the medium through which light waves ripple, this should mean the speed of light differs ever so slightly in the direction Earth is traveling.

Conducted in Cleveland, Ohio, the Michelson–Morley experiment used a piece of kit called a Michelson–Morley interferometer to test differences in speed for a wave of light traveling perpendicular to Earth and one traveling parallel to Earth. Michelson and Morley had expected to observe an interference pattern caused by the differing travel times of the light waves.

That is what happens when light of the same wavelength arrives at a detector at ever so slightly different times, meaning the peaks and troughs of the waves no longer perfectly align. However, to the surprise of the American physicists, no interference was detected. This meant no difference in the travel speed of light, essentially disproving the existence of the ether.

The negation of the luminiferous ether was of vital importance as it opened the door to Albert Einstein's theory of special relativity in 1905 and general relativity in 1915, the latter of which revised our understanding of gravity and led to our knowledge of black holes and gravitational waves well before the experimental observation of such objects.

Other galaxies!

Though scientists realized Earth isn't in the center of the solar system before the birth of the U.S., there was another glaring misconception. It was believed that the Milky Way, first proposed in Immanuel Kant's "Island Universe" theory in 1755, still occupied a unique position in the universe — with the existence of other galaxies a hotly debated topic. The solar system itself was also thought to be at the center of the Milky Way.

In 1785, astronomer William Herschel set about mapping our galaxy, correctly determining the disk-like shape of the Milky Way but incorrectly placing the solar system at its heart. This picture changed in 1918, when American astronomer Harlow Shapley determined that dense groups of stars called globular clusters are centered on a distant core in the direction of the Sagittarius constellation. This placed the solar system off-center in the galaxy. Today we've expanded upon this, moving our planetary system 27,000 light-years away from the Galactic Center and onto one of our galaxy's spiral arms.

It was five years later, in 1923, that the uniqueness of the Milky Way was shattered. Using the 100-inch (2.5-meter) Hooker telescope at the Mount Wilson Observatory, American astronomer Edwin Hubble imaged the Andromeda nebula (Messier 31) and determined that it was at least a million light-years away. Though we now know this distance is closer to 2.5 million light-years, it was still enough to place M31 outside the boundary of the Milky Way.

The fact that the Andromeda nebula is actually the Andromeda galaxy, a distant and separate galaxy from our own, was announced to the public via The New York Times in Nov. 1924. We were no longer alone galactically — but Hubble wasn't done.

The universe is not static

Another assumption at this time was that the universe was static, something supported by Einstein in 1917. However, in 1929, Hubble discovered that the light from distant galaxies was being redshifted. In other words, the wavelengths of light emanating from these sources were being stretched as those wavelengths traveled toward us. This indicated that these galaxies are moving away from us. Convinced of this, Einstein abandoned his model of the static universe.

American scientists weren't done revising our entire picture of the cosmos, however. In 1998, U.S. researchers like Saul Perlmutter, Adam Riess, and Robert Kirshner were part of two international teams of researchers that discovered that not only is the universe expanding, but this expansion is actually speeding up.

Dark energy was introduced as the mysterious force driving this accelerating expansion. It remains today one of the most pressing mysteries of the cosmos.

Possibly by the time the U.S. celebrates its 300th birthday, the mystery of dark matter will have been solved along with other cosmic puzzles such as the nature of dark matter. If this is the case, it is highly likely that U.S. projects like the Hubble Space Telescope, the James Webb Space Telescope, and the upcoming Nancy Grace Roman Space Telescope will put American innovators and scientists at the forefront of these developments, just as their predecessors have been for the last 250 years.

The expansion of the universe is still accelerating under the influence of dark energy, despite recent claims to the contrary, according to new research. This means that dark energy, the mysterious force that dominates the universe, is not weakening but continues to get stronger, considered something of a "cosmological crisis" as it was so against expectations.

In 1998, via the study of cosmic explosions called Type Ia supernovas, astronomers discovered that not only is the universe expanding, but that the speed of that expansion is increasing. "Dark energy" was the name given to the mysterious force driving this accelerating expansion. Since then, scientists have discovered that dark energy accounts for around 70% of the universe's matter and energy.

In November 2025, research was published that suggested the expansion of the universe was slowing, meaning dark energy would be weakening. But this new research suggests that these findings from last year might not be a cosmic hand grenade thrown into the cosmological apple cart, but instead may have actually emerged from a scientific misunderstanding.

"Thankfully, we have averted this crisis, but the mystery about why the rate of expansion of the universe is still accelerating remains," lead author of the new refuting research, Phil Wiseman, from the University of Southampton in the UK, said in a statement. "The previous and well-accepted measurements were, in fact, fine, and our current understanding of the fate of the universe remains robust. By proving our measurements are correct, we can get back to trying to understand what this dark energy actually is, rather than wondering if it exists at all."

The research from 2025 that suggested dark energy was weakening was based upon a reassessment of the brightness of Type Ia supernovas, which occur when a dead star called a white dwarf overfeeds on a companion star. This causes a runaway nuclear explosion of such uniform brightness that it can be used to measure cosmic distances. In fact, these explosions are so uniform that astronomers refer to them as "standard candles."

This prior research determined, incorrectly it now seems, that as the universe has aged, the brightness of Type Ia supernovas had changed, leading to incorrect measurements of distances based on them as well as incorrect estimates of the speed of the universe's expansion. Both of these led to the suggestion that dark energy is weakening.

But Wiseman and colleagues found this previous team had made an error in how they calculated the ages of exploding white dwarfs, finding they had assumed the ages of these stars would be the same as the ages of the galaxies in which they exploded.

They also found the 2025 research hadn't accounted for a common correction used in cosmology that factors in the masses of galaxies in which Type Ia supernovas occur.

"Extraordinary claims require especially careful testing," team member Adam Riess, who in 2011 shared the Nobel Prize for the discovery of dark energy, said. "What we find is that when we calibrate these supernovae, accounting for different host environments and populations, the evidence for cosmic acceleration remains remarkably consistent."

While the challenge to dark energy's growing dominance over the universe seems now to have been refuted, the back and forth on this topic shows how ideas in science aren't dogma and remain open for revision.

"This is how progress is made," team member Mark Sullivan, also from the University of Southampton, said. "Although this idea did not turn out to be correct, it has opened up new ways of thinking about how supernovae explode and how we can measure dark energy more accurately."

The team's research was published on June 10 in the journal Monthly Notices of the Royal Astronomical Society.

One of the most hotly debated mysteries in astronomy is set to continue, as new research fails to rule out self-annihilating dark matter as the source of gamma-ray emissions from the heart of the Milky Way. Known as the Galactic Center Excess, a spherical gamma-ray glow extending out for thousands of light-years from the core of our galaxy, this high-energy light has baffled researchers for over a decade.

While several possible explanations for the Galactic Center Excess have been put forward, including a population of rapidly spinning neutron stars called pulsars, one of the most prevalent has been a specific type of dark matter particle. Dark matter is the mysterious stuff that accounts for 85% of the universe's matter. It is effectively invisible because it doesn't interact with light or with "ordinary" matter composed of atoms. That fact has led to many possible dark matter candidate particles being proposed, including some that self-annihilate. This is akin to what happens when an electron meets its antimatter counterpart, or positron. The two annihilate each other, releasing energy into the cosmos.

For self-annihilating dark matter, these particles would be their own antiparticles, meaning when they interact, they would annihilate and release energy as gamma rays. With dark matter outweighing ordinary matter by a ratio of five to one, one might expect this annihilation to be occurring constantly, flooding the cosmos with gamma rays, but dark matter rarely interacts with itself in this model. Thus, dark matter annihilation is only a factor when this mysterious stuff is densely clustered in a region like the heart of a galaxy.

Unfortunately, investigating the heart of the Milky Way is challenging indeed.

"Interpreting the signal is particularly difficult because the Galactic Center is an exceptionally bright and crowded region of the gamma-ray sky," team member and University of Vienna researcher Florian List said in a statement.

Getting to the point

To investigate if annihilating dark matter could indeed account for the Galactic Center Excess, List and colleagues turned to machine learning trained on more than a million simulated gamma-ray observations. Previous similar approaches had pointed to comparatively bright, unresolved light sources as a potential source of the Galactic Center Excess. However, this new research showed that these point sources, including pulsars, would be extremely faint, and that is good news for scientists who favor annihilating dark matter as the cause of these gamma rays.

That is because, whereas previous research has suggested just a few hundred pulsars could be enough to account for the Galactic Center Excess, these findings indicate that the pulsar population at the heart of the Milky Way would have to be greater than 35,000.

"Our new analysis shows that the sources would have to be so faint that they would be almost indistinguishable from the emission expected from annihilating dark matter," team member Nick Rodd, a scientist at the Lawrence Berkeley National Laboratory, said.

While this research may keep dark matter in the game as a plausible explanation, it far from confirms the annihilation of this mysterious stuff as the source of the Galactic Center Excess. "The origin of the Galactic Center Excess is one of the longest-running debates in astrophysics," List said. "Our work does not show that dark matter is responsible for the signal. However, it suggests that it is still too early to rule out this possibility."

The team's research was published on Thursday (Feb. 5) in the journal Physical Review Letters.

Astronomers have used a technique called echo mapping to detect hints that supermassive black holes, such as the cosmic titan at the heart of the Milky Way, known as Sagittarius A* (Sgr A*), are surrounded by dense clouds and clusters of dark matter. The research could teach us more about this mysterious substance and the environments around supermassive black holes.

Dark matter is the universe's most mysterious stuff, outweighing ordinary matter in the cosmos by a ratio of five to one — but remaining effectively invisible because it doesn't interact with electromagnetic radiation, including the light we use to see. The only way scientists can even infer the presence of dark matter is via its interaction with gravity, and the impact that this interaction has on objects made of traditional matter like stars. For instance, the gravitational effect of dark matter allows stars at the edges of galaxies to whip around at much greater speeds while not flying loose than the visible matter of those galaxies would allow.

This team decided to test the gravitational influence of dark matter at the hearts of galaxies, environments dominated by supermassive black holes which can have masses millions or even billions of times that of the sun. Ordinary matter around these supermassive black holes is often very visible, especially when spiraling into the maw of one of these cosmic titans from a flattened cloud called an accretion disk. This is because the gravitational influence of those black holes generates immense amounts of friction, causing them to grow brightly. That wouldn't work for dark matter; it can't feel friction because it doesn't interact with itself or with ordinary matter, and it can't glow because it doesn't absorb or emit light.

Clearly, dark matter can't be spotted around supermassive black holes even using the most advanced telescopes such as the Event Horizon Telescope (EHT), which has captured glowing rings of material around Sgr A* and around a more distant supermassive black hole that rules the heart of the galaxy Messier 87 (M87).

While discussing the problem of detecting dark matter around supermassive black holes, Mayank Sharma, a physics graduate student at Virginia Polytechnic Institute and State University (Virginia Tech), hit on an interesting solution.

"We could actually test this prediction using a technique in astronomy, which allows you to measure the distance to the surrounding gas by looking for echoes of light," Sharma said in a statement. The technique Sharma refers to is "reverberation mapping," and it has become a trusted method of determining the mass of black holes.

Echoes of dark matter

Reverberation mapping is based upon the fact that as matter falls into a black hole, it releases a burst of energy that causes the accretion disk it comes from to pulse. This pulse of light travels from the accretion disk to gas in the wider environment of the black hole. This gas absorbs that light and also pulses, with this secondary pulse serving as an echo of the first.

Because we know the speed of light, when astronomers see the first pulse of light and then its echo, they can use the time between pulses to estimate the distance between the black hole and the gas on the outskirts of its environment. The size of a black hole and the distance between it and outer gas clouds can be used to determine its mass, and could also be used to determine the mass of dark matter clustered around it.

The team applied their method to 14 different galaxies, finding in five cases that mass increases moving away from the central black hole in a way that couldn't be accounted for by visible matter alone. Despite the early success of this research, it far from proves that supermassive black holes are indeed gathering places for dark matter. The team's findings do point an interesting way forward for the investigation into the universe's most mysterious substance and its most mysterious regions.

"These galaxies are definitely showing a hint that there is extra material that cannot be explained by just the supermassive black hole," Sharma said. "The prospects are exciting."

The team's research was published in the journal Physical Review D.

For decades, scientists have searched for a fifth fundamental force of nature that can explain mysterious aspects of the universe such as dark energy and dark matter. These are pieces of our cosmos that simply can't be accounted for by the four fundamental forces we know of: gravity and electromagnetism as well as the strong and weak nuclear forces.

In addition, while the hunt for this force has been ongoing, researchers have also been desperately hunting for a theory of quantum gravity. That's because quantum gravity can unite the best description we have of the universe on large scales — Albert Einstein's theory of general relativity — and the physics of the subatomic, aka quantum mechanics. Both theories emerged at the start of the 20th century and have been experimentally confirmed time and time again, yet they steadfastly refuse to overlap in a single unified theory.

But now, these two scientific quests have overlapped. New research built a quantum gravity framework — finding that it actually offers clues about potential fifth fundamental forces of nature.

The team's findings reveal that not all potential suggestions for a fifth fundamental force, which would manifest as a small deviation from Isaac Newton's law of gravitation at very small distances and would be described by two parameters: its strength and the range it acts over. In essence, the research could narrow down the search for a fifth fundamental force.

"One of the main challenges was overcoming a primarily conceptual obstacle: quantum gravity is often seen as an extremely abstract topic, almost impossible to connect to observable phenomena," Alfio Bonanno of the National Institute for Astrophysics (INAF) said in an emailed statement translated from Italian. "In some ways, it's like standing in front of a mountain face that everyone considers unscalable. The first step isn't technical, but mental: convincing yourself that a possible path actually exists. This work stems precisely from this idea: seeking a concrete connection between the physics of infinitesimally small scales and phenomena potentially observable in the real world."

The framework of quantum gravity explored by the team is called "asymptotic safety," which asserts that gravity can remain consistent and controlled even at high energies thanks to a halting in the strength of gravitational pull. If this theory is to remain valid at high energy levels, Bonanno and colleagues found that the range and strength of a fifth fundamental force were limited, resulting in an excluded region of these parameters.

"The most exciting aspect is that part of the theoretically excluded region has not yet been explored experimentally," Bonanno said. "This means that future high-precision measurements of gravitation could directly test — and potentially falsify — this class of quantum gravity-inspired models."

Usually, physicists hypothesize new forces and then determine if they could be detected by experiment; this research takes a different approach by ruling out certain possibilities for the characteristics of a proposed force. The fact that much of the region excluded by the team hasn't been explored experimentally lays the groundwork for making precise measurements of gravity to test quantum gravity.

"Our study shows that quantum gravity may not only be a valid theory at extreme and unattainable energies, but may also have concrete and testable consequences at much larger scales," Emiliano Glaviano of the INAF said in the statement. "The physics of infinitesimally small distances could leave observable traces in the macroscopic world: some possible new forces of nature would be ruled out not by experiments, but directly by the fundamental laws of the theory."

This research applies to physics on the tiny scales of quantum physics, where quantum gravity should emerge, to the scales of planetary objects. Thus, traces of this quantum gravity theory or a fifth fundamental force appearing as deviations from Newton's laws should be testable with a wide range of experiments. That includes using a technique called atomic interferometry or quantum sensors to make measurements across the solar system, such as lunar laser ranging, or on wider astronomical scales such as measuring the dynamics of planets.

The team's research was published in the May edition of the journal Physical Review Letters.

The most mysterious and yet ubiquitous stuff in the cosmos, dark matter is effectively invisible. This is simply because it doesn't interact with light. But what if instead of trying to see dark matter, scientists attempted to hear it instead?

New research suggests dark matter could leave a tiny but discernible imprint in the cacophony of ripples in spacetime called "gravitational waves" that ring through the cosmos when two black holes slam together and merge. However, this is only if spinning black holes can "churn" dark matter like cosmic butter. (We'll get to that shortly.)

The team behind this new research suggests that if two black holes merge in a region of space populated by dense dark matter clouds, then the gravitational waves emerging from the event could carry the imprint of dark matter across the universe. And it's possible, they say, that our detectors could find that imprint. This would be akin to someone coughing at a Metallica concert, and that cough being only discernible over the fury of "Seek and Destroy" or "Master of Puppets" with the most sensitive instruments.

Fortunately, when it comes to detecting gravitational waves from colliding black holes, humanity's instruments, such as LIGO (Laser Interferometer Gravitational-Wave Observatory), are getting more and more sensitive all the time. And in preparation for a time when such imprints could become even more easily logged in gravitational wave data, this team developed a method that predicts just what shape a gravitational wave should take when moving through dark matter, rather than empty space.

"Using black holes to look for dark matter would be fantastic," team member Rodrigo Vicente, a researcher at GRAPPA (Gravitation Astroparticle Physics Amsterdam), said in a statement. "We would be able to probe dark matter at scales much smaller than ever before."

I can't believe it's not butter

Dark matter represents such a puzzle because, despite being invisible to us, it still "outweighs" ordinary matter by a ratio of about five to one.

Its lack of interaction with light means it can't be composed of protons, neutrons and electrons — the particles that compose atoms. That's because atoms compose all the "ordinary matter" we see around us, from stars and planets to the device you're reading this article on and our own bodies. In other words, atoms do interact with light (more technically, electromagnetic radiation). In fact, the only way astronomers know dark matter exists is via its interaction with gravity and the way this interaction curves spacetime, indirectly influencing ordinary matter and light.

With this knowledge, scientists have been hunting for particles outside the Standard Model of particle physics that could account for dark matter. These particles have a wide range of potential masses and properties, with one hypothetical particle being the "light scalar" proposed to have a mass much smaller than that of an electron. One characteristic of the light scalar would be the fact that dark matter composed of these particles would act like coordinated waves around black holes.

Around a spinning black hole, rotational energy would be transferred to light scalar dark matter, amplifying its density, almost like a paddle churning cream into butter. If this dark matter "butter" gets dense enough, it could affect gravitational waves from merging black holes, leaving a telltale imprint.

After determining what this signature would look like, Vicente and colleagues searched through data gathered by LIGO and its fellow gravitational wave detectors, KAGRA (Kamioka Gravitational Wave Detector) and Virgo, focusing on 28 of the clearest signals from merging black holes. Of these, 27 appeared to have come from mergers that occurred in the relative vacuum of space. One signal, however, GW190728, first heard on July 19, 2019, and the result of merging binary black holes with a combined mass of 20 times that of the sun and located an estimated 8 billion light-years away, seemed to carry the telltale trace of this merger occurring in a region of dense, "buttery" dark matter.

The team behind this research is quick to point out that this can't be considered a positive detection of dark matter, but does say it gives us a hint at what to look for and thus where to direct follow-up investigations — something that could be increasingly useful as dark matter detectors on Earth continue into their fifth operating run with boosted sensitivity.

"We know that dark matter is around us. It just has to be dense enough for us to see its effects," said team leader Josu Aurrekoetxea, of the Massachusetts Institute of Technology (MIT) Department of Physics. "Black holes provide a mechanism to enhance this density, which we can now search for by analyzing the gravitational waves emitted when they merge."

The team's results were published on Tuesday (May 12) in the journal Physical Review Letters.

Using artificial intelligence and data from the groundbreaking Vera C. Rubin Observatory, scientists are reconsidering our knowledge of "standard candles" in the cosmos. These are objects that result from explosions provoked by dead stars that act like cannibals — and they help us measure distances across the universe.

These standard candles are also called Type 1a supernovas, and their distance-measuring role is integral to measuring the rate at which the universe is expanding. This means they're also integral in our understanding of how this expansion is accelerating due to the effect of dark energy, the mysterious force helping to push our cosmos apart in every direction.

The research team's approach to looking at these Type 1a supernovas involves what's known as a combined inference and galaxy-related standardization, or CIGaRS, framework. It differs from a more standard approach because, instead of using spectroscopic observations — which revolves around analyzing light signatures — it looks at actual images and a mathematical analysis. This approach, the team explains, allows astronomers to determine more about the age and concentration of heavy elements — collectively known as "metals" in astronomy — in the stars that explode in Type 1a supernovas. That's important because it can reveal the stars' distances more precisely.

"A powerful way of modeling the universe is to simulate it in the computer," research team member Raúl Jiménez of the University of Barcelona said in a statement. "This provides a way to vary all possible parameters at the same time to predict what universe we live in.

"Furthermore, by having this capacity, one can look into possible 'unknown unknown' systematics to understand their effect. The impact of these systematics in our inference is arguably the most important missing ingredient in current approaches to model the universe."

Recapping the dark energy problem and cannibal stars

Our discovery of dark energy began with the death of stars of similar sizes to the sun and their transformations into smoldering stellar embers called white dwarfs. The sun will end its life as a white dwarf in around 6 billion years, fading alone in a cosmic graveyard that was once our solar system. However, when stars have a binary partner, white dwarfs can spring back to life like cosmic vampires by stripping material off these companion stars.

This stellar cannibalism ends with a runaway nuclear blast that usually wipes out the white dwarf entirely: The Type 1a supernova.

Here's the beauty of the destruction, though. These Type 1a supernova explosions have been considered so uniform in nature (more on this in a moment) that analyzing their light output tells researchers how far away they are and how fast they are moving due to the expansion of the cosmos.

In 1998, two teams of astronomers independently used Type 1a supernovas to discover that not only is the universe expanding, but it is doing so at an accelerating rate. The placeholder name for the force driving this acceleration is dark energy.

Since the late 1990s, the situation has just gotten messier and messier. For example, we now know that dark energy, whatever it is, dominates the cosmos, accounting for around 68% of the universe's matter and energy budget. Plus, we know dark energy only started to dominate around 4 billion years ago when the universe was around 9 billion years old and when the Big Bang-driven expansion had been halted by matter and its gravitational effect.

To get a picture of why this is troubling, consider this: Imagine pushing a child on a swing, watching her slow down and come to an almost complete stop, like the Big Bang-driven expansion. Then, the swing speeds up and keeps moving faster and faster, seeming to move without any push. That is what dark energy is doing to the universe.

It is therefore little wonder scientists like Jiménez and colleagues want to get to the bottom of dark energy. This puzzle is widely considered to be the biggest mystery in modern cosmology.

But here's the thing: Remember the point about Type 1a supernovas seeming identical? Researchers have recently discovered that this doesn't always ring quite true.

Not-so-standard candles?

Over the last 20 or so years, astronomers have found that the brightness of Type 1a supernovas has a small dependence on the galactic environment in which they explode. When these explosions erupt in large or old galaxies, they look slightly different from those in smaller or younger galaxies.

While this effect has been tackled by making approximating adjustments, it still hinders the precision of the distance measurements provided by these cataclysmic standard candles. This team approached that issue by modelling all factors associated with supernovas, including the nature of their host galaxies, any dust that may dim their light output, the frequency of these explosions over time, and, indeed, the expansion of the universe, all at once. The result was a single, self-consistent model uniting elements physically and statistically. The team was also able to model tens of thousands of Type 1a supernovas at one time.

The result is a method that can estimate galaxy distances very accurately using only images. This is going to become crucial when the Legacy Survey of Space and Time (LSST), conducted by the Rubin Observatory from its mountaintop perch in Chile, starts delivering observations of unprecedented numbers of supernovas. Something the CIGaRS framework is uniquely equipped to deal with.

"Unlike other frameworks, which require analytic simplifications, our no-compromise end-to-end simulation-based inference approach is uniquely capable of extracting the full cosmological and astrophysical information from the Rubin Observatory's hard-earned data, while avoiding the pitfalls of selection and modelling biases," team leader Konstantin Karchev of the University of Barcelona said in the statement.

These results were published on Wednesday (May 6) in the journal Nature Astronomy.

A new type of self-interacting dark matter could provide solutions to three very different cosmic puzzles, new research suggests.

The first mystery that could be solved involves an ultradense clump of matter detected in the system JVAS B1938+666, which is gravitationally lensed, or visibly distorted, thanks to a quirk of general relativity. The second has to do with a visible "scar" in a stream of stars called GD-1. It basically looks like a dense, invisible object ripped through the stream. And finally, there is the confusing formation of an unusual star cluster named Fornax 6 in the Fornax satellite galaxy of the Milky Way, which could have occurred if a dense patch of dark matter acted as a gravitational trap capturing passing stars.

The new research argues that if dark matter interacts with itself, that could explain away all three of these unique situations." What's striking is that the same mechanism works in three completely different settings — across the distant universe, within our galaxy, and in a neighboring satellite galaxy," Hai-Bo Yu of the University of California, Riverside and the Center for Experimental Cosmology and Instrumentation, said in a statement. "All show densities that are difficult to reconcile with standard model dark matter but arise naturally in self-interacting dark matter."

But what does it really mean for dark matter to "interact" with itself, and why would that be a deviation from the "standard" picture of this mysterious substance?

Anti-social dark matter can't explain these mysteries

First, let's go through a quick recap of what dark matter really is.

Dark matter accounts for around 85% of the matter in the universe, meaning it "outweighs" the ordinary matter that comprises stars, planets, moons, and our bodies by a ratio of around five to one. Scientists know dark matter can't be made up of protons, electrons and neutrons that compose the atoms that make up everything we see around us, because those particles interact with light (more accurately, electromagnetic radiation) — and whatever composes dark matter doesn't.

This also means dark matter is effectively invisible to us, only detectable via its interaction with gravity and the knock-on effect this has on everyday matter and light. Separately, the best theory of cosmic evolution we have so far is the standard model of cosmology, also known as the lambda cold dark matter (LCDM) model. In the LCDM model, dark matter is "cold," meaning its particles move slowly and don't collide when they meet, instead passing through each other without interacting like anti-social cosmic ghosts.

Thus, unlike cold dark matter, self-interacting dark matter particles can collide with each other, exchanging energy and momentum. These interactions can result in so-called "gravothermal collapse," creating dense, compact cores of dark matter.

"The difference is like a crowd of people who ignore each other versus one where everyone is constantly bumping into one another," Yu said. "In self-interacting dark matter, these interactions can dramatically reshape the internal structure of dark matter halos. Dark matter that interacts with itself can become dense enough to explain these observations."

"The difference is like a crowd of people who ignore each other versus one where everyone is constantly bumping into one another," Yu said. "In self-interacting dark matter, these interactions can dramatically reshape the internal structure of dark matter halos."

In short, this recipe of self-interacting dark matter allows for dense dark matter cores with morphology that could explain the strange aspects of the astronomical bodies such as the ultradense clump of matter observed in JVAS B1938+666 and the "scar" of GD-1 — but non-interacting dark matter can't. "Dark matter that interacts with itself can become dense enough to explain these observations," Yu added.

The team's research was published on April 9 in the journal Physical Review Letters.

The Dark Energy Spectroscopic Instrument (DESI) has completed its five-year mission to build the largest 3D map of the cosmos ever constructed in order to investigate dark energy, the mysterious force driving the accelerating expansion of the universe. The 3D map was completed ahead of schedule on Tuesday night (April 14), but DESI is far from done. With this map in hand, it'll continue to probe some of the greatest mysteries in cosmology.

"DESI has exceeded expectations. It is a big deal because the DESI team was able to complete a heavily ambitious survey program on schedule and on budget. It wasn't at all clear that we would achieve this years ago when we first planned DESI and applied for support from the Department of Energy," Klaus Honscheid, lead scientist of DESI instrument operations and a professor at The University of Ohio, told Space.com.

DESI, composed of 5,000 fiber optic eyes mounted on the Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory in Arizona, exceeded expectations by observing 47 million galaxies and quasars — which are central galactic regions powered by feeding supermassive black holes — as well as more than 20 million nearby stars. Originally, scientists predicted that about 34 million galaxies and quasars would compose the completed DESI dataset when it began operations in May 2021. We're seeing a sixfold increase on previous observations of galaxies and quasars.

"Our ability to complete the survey in five years was challenged more than once. Everyone on the operations team worked incredibly hard to keep the survey progressing with high efficiency. And I think rightly so, we are all very proud that we actually achieved this goal," Honscheid said.

Researchers will be eager to get their hands on the completed five years' worth of DESI data. Using just year one observations, researchers already saw tantalizing evidence that dark energy is even stranger than predicted, suggesting we may need to revise the standard model of cosmology, the current best picture we have of how the universe evolved to its current state.

Already making waves

Dark energy represents such a mystery because, though accounting for around 70% of the universe's matter and energy budget, scientists have no idea what it actually is. Discovered in the late 1990s, dark energy is really just a placeholder name for whatever force is pushing galaxies apart faster and faster.

"The mystery of dark energy arises from observations from the combination of several cosmological probes, including baryon acoustic oscillations (BAO), cosmic microwave background, and Type 1a supernovas," Nathalie Palanque-Delabrouille, DESI collaborator and a scientist at Berkeley Lab, told Space.com. "None of these probes yet has the sensitivity to resolve the mystery of dark energy on its own. The data DESI has already gathered will allow us to strengthen our findings and clarify what options remain possible."

After analyzing the first year of data from DESI in April 2024 and tracking the effect of dark energy over 11 billion years of cosmic history, scientists revealed they had found tantalizing hints that dark energy is weakening. If confirmed by the full DESI map, this represents a major and exciting discovery, as the standard model of cosmology, also known as the Lambda Cold Dark Matter (LCDM) model, predicts that dark energy should be constant, meaning it shouldn't fluctuate in strength.

"This is a major paradigm shift. All data up to now were compatible with a standard cosmological model where the accelerated expansion of the universe was caused by a cosmological constant," Nathalie Palanque-Delabrouille, DESI collaborator and scientist at Berkeley Lab, told Space.com. "The weakening acceleration observed by DESI can no longer be explained with a cosmological constant. This could be the most interesting discovery in cosmology since that of dark energy itself."

The first papers based on DESI's full five-year program are expected to appear throughout 2027. Even before these findings begin to drip out, the completion of DESI's initial mission represents a major scientific milestone.

"One of the most significant aspects on the science side is the remarkable cohesion of the large collaboration: over 900 scientists, including about a third graduate students, all working towards the same goals. The work is performed across 14 countries and 75 institutions, yet the data are analyzed in a timely fashion, and DESI has already published key results with its year-1 and year-3 data samples," Palanque-Delabrouille said. "What surprised me, or rather impressed me, is that DESI continues to run on schedule, even to be ahead of schedule, despite the pandemic and the Contreras fire that swept through the Kitt Peak observatory in 2022.

"DESI's pace is truly amazing."

The team's research was published across two papers in the journal Astronomy & Astrophysics.

All galaxies are dominated by dark matter, an invisible "stuff" that outweighs all of the matter comprising stars, planets, and moons by around five to one. But in some galaxies, dark matter takes this domination to the extreme. Using the Hubble Space Telescope along with the Euclid Space Telescope, astronomers have discovered what seems to be one of the most heavily dark-matter-dominated galaxies ever seen.

This "dark galaxy," officially designated CDG-2, is located around 245 million light-years away. Unlike regular galaxies, which are bright and prominent even across vast cosmic distances, dark galaxies like CDG-2 are faint, nearly invisible and ghost-like thanks to a sparse smattering of stars and their huge quantity of dark matter.

The team behind the discovery of this galaxy found that, unlike standard galaxies, in which dark matter outweighs ordinary matter by a ratio of five to one, dark matter accounts for a staggering 99% of the mass of CDG-2.

Dark matter is effectively invisible, because unlike protons, neutrons, and electrons  — the particles that comprise everyday matter  — whatever composes dark matter doesn't interact with electromagnetic radiation, that's "light" to you and me. Scientists have been able to determine that galaxies are ruled by dark matter, with dense central cores and halos that extend far beyond visible gas and dust, due to the fact that dark matter does interact with gravity.

This gravitational influence then influences visible matter and light, a knock-on effect which astronomers can see. Even so, dark galaxies are extremely tough to detect.

The discovery of CDG-2 began when a team of astronomers investigated tight groupings of stars called globular clusters, which can often indicate the presence of a hidden population of dim stars in their vicinity. This led to the confirmation of ten faint low-brightness galaxies and two dark galaxy candidates.

To confirm the existence of one of these dark galaxies, the researchers turned to Hubble, Euclid, and the Subaru Telescope in Hawaii.

Hubble data confirmed a tight grouping of four globular clusters in the Perseus galaxy cluster, located around 300 million light-years away. Further observations from Hubble, along with data from Euclid and Subaru, revealed a faint glow around these globular clusters, which served as evidence of a hidden, near-invisible galaxy lurking behind these globular clusters. CDG-2 had revealed itself.

"This is the first galaxy detected solely through its globular cluster population," team leader David Li of the University of Toronto, Canada, said in a statement. "Under conservative assumptions, the four clusters represent the entire globular cluster population of CDG-2."

Li and colleagues performed a deeper analysis of CDG-2, finding that it has a brightness equivalent to that of around 6 million sun-like stars. They determined that around 16% of this brightness was accounted for by the overlying globular clusters. The normal matter in this dark galaxy is thought to have enabled star formation in its past, but the team theorizes these stellar bodies have been stripped away by gravitational interactions with other galaxies. The globular clusters used to detect CDG-2 were able to withstand this gravitational interference due to how densely packed with stars they are, leaving them the only tracers of a now ghostly galaxy.

The team's results were published in The Astrophysical Journal Letters.

The universe is a vast, unseen loom, weaving galaxies into an intricate cosmic web through invisible threads of matter. This cosmic web is the fundamental scaffolding of everything we see, dictating where galaxies form and how they evolve. Much of this architecture remains a mystery, its delicate pathways hidden, and uncovering these cosmic threads requires new eyes and persistent effort.

But a new observation has helped us trace one in the Ursa Major Supergroup. In a preprint paper published on the open source repository arXiv, a team of scientists pinpointed a group of galaxies that stretch out in a line spanning nearly four light-years, a discovery that unveils a delicate, thin filament – a hidden pathway, dominated by dark matter, where galaxies are born and evolve in synchronized dances.

It's a glimpse into the universe's secret architecture, revealing how even the most subtle cosmic structures orchestrate the grand ballet of creation, guiding the destiny of galaxies across the eons. We are learning how the universe truly puts itself together, one subtle thread at a time.

Astronomers have long understood that the universe isn't a uniform soup of stars and gas. It's organized into a gigantic, intricate network, much like a spider's web. This is the cosmic web, a structure with dense knots of galaxies, long strands connecting them, and vast, empty spaces. Gravity, acting over billions of years, pulls matter together to form this architecture. Much of this matter is something we cannot directly observe: dark matter.

Imagine huge amounts of invisible stuff in space. We can't see it because it doesn't interact with light. But its gravity pulls on everything we can see, making objects move in ways they wouldn't otherwise. It's a hidden gravitational scaffolding that shapes the universe. These long strands, filaments of the cosmic web, are dominated by this unseen dark matter. They act as cosmic highways, guiding gas flow that feeds new generations of stars and galaxies.

Powerful new instruments are uncovering the universe's secrets. China's FAST telescope, the Five-hundred-meter Aperture Spherical radio Telescope, did just that recently when its incredible sensitivity allowed astronomers to peer into previously faint or diffuse regions. Using FAST HI observations, a team identified a group of galaxies with a nearly linear distribution extending from northeast to southwest. This finding represents a coherent structure: galaxies lined up in space. It's like finding a single, almost invisible thread woven into a giant, dusty tapestry.

This discovery reveals a delicate thin filament, a previously unnoticed cosmic pathway. Identifying this distinct, linear arrangement provides direct observational evidence for these predicted, yet often hard-to-spot, components of the cosmic web. This shows the power of new instruments, observing what was once theoretical. These linear groupings offer tangible proof of the cosmic web's intricate design, especially its more subtle strands.

A line of galaxies, a cosmic filament, carries significant implications for understanding the universe's architecture. These linear arrangements are not random. They hint at the unseen cosmic web, showcasing how dark matter guides galaxy formation. Dark matter's gravitational pull within these filaments acts like a cosmic funnel, drawing in gas and dust, providing raw materials for new stars and galaxies.

This observation shows how subtle cosmic architecture directs galaxies' destinies, influencing their formation, interactions, and evolution. Just like living organisms, galaxies aren't static; they are born, grow, change their appearance, and sometimes even merge with other galaxies over billions of years.

This newly identified filament serves as a prime example of a cosmic nursery, where dark matter's gravitational pull creates conditions for galaxies to coalesce and begin their journey. It implies even these faint structures play a crucial role in cosmic development. We are only just beginning to grasp their full extent and long-term role in galaxy evolution.

New research suggests the supermassive black hole at the heart of the Milky Way is actually a tremendously massive yet compact clump of dark matter.

Scientists say this clump would exert the same gravitational effects currently attributed to the Milky Way's supermassive black hole, Sagittarius A* (Sgr A*). That includes the violent and rapid dance of stars taking place at the Galactic Center, in which so-called "S-stars" race around the compact heart of our galaxy at speeds as great as 67 million miles per hour (30,000 kilometers per second). For context, that's around 10% of the speed of light. This dark matter clump, the team says, would also account for the orbits of the dust-shrouded bodies, or "G-sources" located in the Galactic Center.

However, this substitution of a black hole for dark matter only works if dark matter is composed of ultra-light particles that are part of the "fermion" family. This would grant the dense cluster at the heart of the galaxy the ability to form a cosmic structure that matches those observed characteristics of the Galactic Center.

Fermionic dark matter is proposed to be capable of forming a structure that consists of a super-dense, compact core with so much mass that it mimics a supermassive black hole with a mass equivalent to 4.6 million suns, the research team says. That core would be surrounded by a vast and diffuse halo stretching out far beyond the visible matter of the Milky Way — but acting as a single unified entity. This is a structure that other recipes of dark matter can't replicate.

"We are not just replacing the black hole with a dark object; we are proposing that the supermassive central object and the galaxy's dark matter halo are two manifestations of the same, continuous substance," team member Carlos Argüelles, of the Institute of Astrophysics La Plata, said in a statement.

Seeing is believing … but what are we seeing?

The theory, proposed by Argüelles and colleagues, is strongly based on observations conducted by the European Space Agency's star tracking mission Gaia, released as part of the project's third data drop in June 2022.

Gaia allowed the team to precisely map the rotation and orbit of stars and gas in the outer halo of the Milky Way, revealing a slowdown of our galaxy's rotation curve: the so-called Keplerian decline. This team thinks the Keplerian decline can be explained by the diffuse outer halo they saw, which is a factor in their model and one that, as we now know, adds support to the fermionic model of dark matter.

In the standard model of cosmology, also known as the Lambda Cold Dark Matter (LCDM) model (the best description we have of the universe), dark matter is "cold," which means its particles move at speeds significantly slower than the speed of light.

Cold dark matter forms an extended halo tail that struggles to account for the slowdown observed by Gaia. The fermionic model, on the other hand, predicts a tighter and more compact halo tail that could cause Keplerian decline. Remember, in the Sgr A* model, dark matter at the heart of the Milky Way isn't connected in a single structure to the outer halo, thus that tail isn't present in this model.

"This is the first time a dark matter model has successfully bridged these vastly different scales and various object orbits, including modern rotation curve and central stars data," Argüelles said.

So far, so good. The theory that our galaxy may have a clump of dark matter rather than a black hole in its center appears to be fairly credible. However, there is a 4.6 million solar mass elephant in the room: namely, the image of Sgr A* captured by the Event Horizon Telescope (EHT) and revealed to the public in May 2022. Still, the team says their fermion dark matter model can account for this.

Before diving into that explanation, it is worth considering what we actually see when we look at the EHT image of what we all currently assume to be Sgr A*.

The glowing golden ring in this image is actually superhot matter whipping around whatever lurks at the heart of the Milky Way. What we actually see in this image isn't a black hole at all, understandable because black holes are surrounded by a light-trapping surface called an event horizon; there's no way we could directly see Sgr A*. What we can see, though, is the shadow the black hole casts.

Yet in 2024, researchers demonstrated that a dense core of fermionic dark matter could actually cast a shadow that is similar to that seen in the EHT image. The core would be invisible like a black hole because dark matter famously doesn't interact with light.

"This is a pivotal point," said team leader Valentina Crespi of the Institute of Astrophysics La Plata. "Our model not only explains the orbits of stars and the galaxy's rotation but is also consistent with the famous 'black hole shadow' image. The dense dark matter core can mimic the shadow because it bends light so strongly, creating a central darkness surrounded by a bright ring."

Though the team has statistically compared their dark matter model to the accepted model of a supermassive black hole at the heart of the Milky Way, and the former was able to replicate the behavior of S-stars, G-sources, the structure of our galaxy and the black hole shadow, the researchers emphasize it is definitely still early days for this theory.

The team's research does lay down a roadmap for future observations using the Very Large Telescope (VLT) to hunt for photon rings at the heart of the Milky Way, which will be present for Sgr A*, but absent if the central dominating body of our galaxy is a dense clump of dark matter.

Clearly, Sgr A* isn't ready to relinquish its throne at the heart of the Milky Way to dark matter just yet.

The team's research was published on Feb. 5 in the journal Monthly Notices of the Royal Astronomical Society (MNRAS).

New research suggests that dark matter, the universe's most puzzling and mysterious substance, may not exist. But removing dark matter from our cosmological models could hinge on the possibility that gravity behaves differently on very large scales, one scientist says.

Dark matter has been a thorn in the side of physicists because, despite outweighing ordinary matter by a ratio of 5 to 1, it remains effectively invisible. That's because it doesn't interact with light, or more technically, electromagnetic radiation. Because the particles that comprise the atoms that make up stars, planets, moons, living things, and everything we see around us, do interact with light, scientists have been searching for particles that could make up dark matter. However, this addition to particle physics, which has thus far eluded all attempts to uncover it, isn't needed if we are wrong about how gravity behaves on galactic scales. At least, that is what Naman Kumar of the Indian Institute of Technology suggests.

"The mystery of dark matter — unseen, pervasive, and essential in standard cosmology — has loomed over physics for decades," Kumar wrote for Phys.org. "In new research, I explore a different possibility: Rather than postulating new particles, I propose that perhaps gravity itself behaves differently on the largest scales."

The only reason that scientists have inferred the presence of dark matter is that this strange matter does interact with gravity. In fact, the first hint of dark matter came from the fact that galaxies were observed to be spinning so rapidly that if the gravity of their visible matter was the only force acting to keep them together, they would have flown apart long ago.

Another line of evidence comes from a phenomenon called "gravitational lensing," which occurs when the usually straight path of light is curved by a dent in the fabric of space generated by objects of great mass. This deflection has been found to be too extreme to be accounted for by the visible matter in lensing galaxies. Hence, physicists have inferred that galaxies are embedded with vast haloes of dark matter that extend far beyond their haloes of stars.

The fact that the only evidence for dark matter comes from its gravitational effect on space and by extension everyday or "baryonic" matter explains why a modified theory of gravity could do away with the need for dark matter to exist.

Don't be a square

To investigate this, Kumar looked at gravity through the lens of quantum field theory and at very small scales equivalent to the wavelength of infrared light, a so-called "infrared running scheme." This involved not assuming that Newton's gravitational constant, or "Big G," is allowed to change or "run" at different length scales.

"What emerged is a compelling theoretical case for a scenario in which gravity's effective strength subtly shifts over galactic distances," Kumar wrote.

Gravity is just one example in physics of an "inverse square law" of 1/r^2, meaning that its strength falls off by the square of the distance from a source; when the distance from a gravitating body doubles, then its gravity becomes four times weaker. If the distance is tripled, then the gravitational influence becomes nine times weaker.

Considering his infrared running scheme, Kumar found a gravitational potential that deviates from the usual inverse force law, leading to a long-range force of 1/r. This can lead to the type of rotation seen for galaxies that is currently attributed to dark matter halos.

"These results suggest that the infrared running scenario could account for galaxy rotation without invoking a dominant cold dark matter component," Kumar explained.

As you might expect, because dark matter is considered to account for 85% of the matter in the universe, it stands to reason that removing it from our models of the cosmos has significant implications for understanding how the universe evolved and continues to evolve. However, Kumar's model may fit well with current expectations and observations.

"In the early universe — at the time of the cosmic microwave background and during structure formation — any change in gravity must be small enough to avoid conflict with precision cosmological measurements," Kumar wrote. "Within the infrared running framework, corrections grow slowly with scale and time, preserving agreement with early-universe constraints while becoming relevant only at later epochs and large scales."

The next step for Kumar's theory of infrared-running gravity will be to see how it compares to measurements of gravitational lensing and the gathering of galaxy clusters, currently thought to occur around a framework of dark matter.

"My work opens a path toward understanding dark matter phenomena not as missing particles, but as a subtle feature of gravitation itself — a deep consequence of scale dependence in a quantum field theory of gravity," Kumar concluded. "Although this approach does not yet fully replace dark matter in the cosmological standard model — especially in explaining detailed structure formation and lensing data — it highlights gravity's possible hidden complexity and invites a reevaluation of where dark matter effects originate."

Kumar's research was published in the journal Physical Review Letters B.

Using the James Webb Space Telescope, astronomers have built a detailed map of dark matter, showing the density of this mysterious stuff across a field of view that encompasses around 800,000 galaxies.

Dark matter is so puzzling to scientists because it doesn't interact with electromagnetic radiation, or simply light,, and is thus effectively invisible to us. This tells researchers that dark matter isn't just difficult-to-see ordinary matter made up of protons, neutrons and electrons, which are particles that do interact with light. Hence, the search for particles that could comprise dark matter has been a complicated one. To make matters even more complex, these particles appear to outweigh particles that comprise ordinary matter in the cosmos by a ratio of five to one.

Fortunately, dark matter does interact with gravity, therefore influencing the very fabric of space and time. And the curvature of space caused by large concentrations of dark matter — like dark matter haloes that envelope galaxies and galactic clusters — can influence the passage of light in a process called gravitational lensing first predicted by Albert Einstein back in 1915. It is through its gravitational influence that astronomers were able to use the James Webb Space Telescope (JWST) to build this new map of dark matter.

The area of the sky analyzed with this investigation is around 2.5 times the size of the full moon (as seen from our vantage point on Earth) and located in the constellation of Sextans. The JWST studied this region for around 255 hours with its Near-Infrared Camera (NIRCam) instrument as part of the Cosmic Evolution Survey (COSMOS).

COSMOS is conducted by around 15 different telescopes, including the JWST's trusty sibling the Hubble Space Telescope. These eyes on the universe all repeatedly study a larger section of the sky equivalent to around 10 full moons. This repetition with instruments that see the cosmos in different ways allows scientists to investigate how galaxies grow, with Hubble and JWST data helping to unravel the role dark matter plays in things like galactic evolution.Additionally, Hubble observed the same region involved in the new study back in 2007, and the section has since been investigated by many other ground-based telescopes independently. But the immense sensitivity of the JWST has helped scientists produce a map with around 10 times more galaxies than those produced by ground telescopes and twice as many as seen in the Hubble map.

Using these JWST observations, the team inferred the distribution of dark matter using "weak gravitational lensing" in particular, which is the subtle distortion of light from thousands of background galaxies caused as it passes warped space caused by concentrations of dark matter.

Additionally, observing the region with the JWST's other main instrument, Mid-Infrared Instrument (MIRI), allowed the researchers to better measure the distances to the galaxies in this section of the sky.

The new dark matter map is just another example of how the JWST is revolutionizing our view of space, both near and far, while redefining our understanding of familiar bodies as well as the most mysterious aspects of the cosmos.

Scientists have been gifted with a clearer picture of the expansion of the universe and dark energy, the mysterious force driving the acceleration of this expansion, than ever before. This comes courtesy of the analysis of six years' worth of data collected by the Dark Energy Camera (DECam) mounted on the U.S. National Science Foundation Víctor M. Blanco 4-meter telescope.

The data analysed consists of 758 nights of observations of one-eighth of the sky conducted by the Dark Energy Survey (DES) Collaboration between 2013 and 2019, during the deep, wide-area survey of the sky conducted using the 570-megapixel DECam, which recorded information from 669 million galaxies located billions of light-years from Earth.

This analysis represents the first time the four separate methods of studying dark energy have been united as one. The results doubled the strength of the constraints on the effect of dark energy, an essential step toward discovering the true nature of this mysterious force that dominates the universe.

"These results from DES shine new light on our understanding of the universe and its expansion," Regina Rameika, Associate Director for the Office of High Energy Physics in the Department of Energy’s Office of Science, said in a statement. "They demonstrate how long-term investment in research and combining multiple types of analysis can provide insight into some of the universe’s biggest mysteries."

An expanding problem

The first hints of dark energy were uncovered in 1998 when two separate teams of astronomers observed distant supernovas, finding that the further away they were, the faster they were receding away from Earth. That not only confirmed that the universe is expanding as Edwin Hubble suggested a century ago, but shockingly revealed that this expansion is accelerating. Dark energy is the placeholder name given to whatever is driving this acceleration. In the 28 years since that discovery, scientists have determined that dark energy accounts for around 68% of the total energy and matter budget of the cosmos. It has also been discovered that dark energy hasn't always dominated the 13.8 billion-year-old universe in this way; its effect only "kicked in" and overwhelmed the attractive force of gravity at large scales between 3 and 7 billion years ago. These findings have only emphasised the need to understand what dark energy is.

This new analysis considered Type-Ia supernovas, the same type used to first discover dark energy, in addition to three other probes of cosmic structure and expansion. Those other phenomena are so-called weak gravitational lensing, a phenomenon that occurs when light from a background source passes an object of great mass and is curved; the clustering of galaxies; and so-called baryon acoustic oscillations, fluctuations of density in the early universe caused by pressure waves frozen into space around 380,000 years after the Big Bang. "It is an incredible feeling to see these results based on all the data, and with all four probes that DES had planned," DES Collaboration member Yuanyuan Zhang, of NOIRLab, said. "This was something I would have only dared to dream about when DES started collecting data, and now the dream has come true."

Using the data provided by DECam and the techniques described above, the DES team reconstructed matter distribution over the past 6 billion years of cosmic history. They then compared these results against two of the prevailing models of the universe. These are the standard model of cosmology, also known as the Lambda Cold Dark Matter (LCDM) model, in which dark energy is stable over time; and the extended model (wCDM), in which dark energy is allowed to evolve over time.

The DES results conformed well to the LCDM, but also fit nicely with the wCDM.

But there is one parameter that these new results found to be off in comparison to both of these cosmic models: how matter in the modern universe is predicted to cluster based upon measurements of the early universe. These findings not only confirmed that modern galaxies don't cluster as either the LCDM or the wCDM predicts, but the difference between observations and theory became even more pronounced.

The next step for DES will be to combine DECam data with observations of around 20 billion galaxies from the recently completed Vera C. Rubin Observatory when it begins its decade-long Legacy Survey of Space and Time (LSST).

This should present an even clearer picture of the history of the universe and the nature of dark energy.

"DES has been transformative, and the Vera C. Rubin Observatory will take us even further," Chris Davis, National Science Foundation Program Director, said. "Rubin's unprecedented survey of the southern sky will enable new tests of gravity and shed light on dark energy."

The team's research has been submitted to the journal Physical Review D and is available on the paper repository site arXiv.

New research suggests that dark matter, the universe's most mysterious "stuff," may actually have been born "hot." If this is the case, the best current model we have of cosmic evolution, the standard model of cosmology, also known as the Lambda Cold Dark Matter (LCDM), may need serious revision or overwriting altogether, altering the rules of the epic game of hide and seek that has been ongoing between dark matter and scientists for decades.

Dark matter is a headache for researchers because it doesn't interact with electromagnetic radiation, light, in layman's terms. This not only makes dark matter effectively invisible, but it also means that scientists know it can't be made of the electrons, protons, and neutrons that compose the atoms making up everything from the most massive stars down to the tiniest bacteria, because they do interact with light. Couple this with the fact that dark matter outweighs ordinary matter in the universe by a ratio of five to one.

This mystery has sparked a search for candidate particles for dark matter beyond the standard model of particle physics. Thus far, this search has favored "cold" dark matter, which doesn't refer to temperature but instead references the speed at which the particles move (cold meaning much slower than light, hot meaning moving at speeds approaching light). In the standard picture, cold dark matter emerges from the hot and dense soup of energy that filled the early universe.

The new research suggests an alternative origin. Dark matter could have instead been born extremely hot, opening up alternative possibilities of how it interacts with everyday matter.

The team proposes that incredibly hot dark matter moving at near-light speeds could have been born in the universe during a period called post-inflationary reheating. This refers to the point at which the inflation field driving the rapid initial expansion of the universe decayed and transformed into a hot and incredibly dense "soup" of radiation and particles.

"Dark matter is famously enigmatic. One of the few things we know about it is that it needs to be cold," research leader Stephen Henrich, of the University of Minnesota's School of Physics and Astronomy, said in a statement. "As a result, for the past four decades, most researchers have believed that dark matter must be cold when it is born in the primordial universe.

"Our recent results show that this is not the case; in fact, dark matter can be red hot when it is born but still have time to cool down before galaxies begin to form."

Henrich and his colleagues demonstrated that dark matter could stop significantly interacting with ordinary matter and electromagnetic radiation while still very hot and thus moving at speeds approaching that of light, a process called "decoupling." If produced during post-inflationary reheating, this would give dark matter plenty of time to cool off and start acting like cold dark matter, assisting in the formation of the first galaxies by forming gravitational waves into which ordinary matter clusters.

The concept could resurrect one of the earliest and simplest candidates for dark matter, low-mass neutrinos, which were ruled out around four decades ago because it was thought they would have wiped out galactic-scale structures rather than promoting them.

"The neutrino became the prime example of hot dark matter, where structure formation relies on cold dark matter," team member Keith Olive, also of the University of Minnesota's School of Physics and Astronomy, said. "It is amazing that a similar candidate, if produced just as the hot Big Bang universe was being created, could have cooled to the point where it would, in fact, act as cold dark matter."

The team will now attempt to produce and observe these particles using experiments on Earth, including tests conducted with powerful particle accelerators, as well as detecting them in the early universe. This investigation could not only reveal the true nature of dark matter, but it could also help scientists build a clearer picture of one of the most crucial, yet mysterious, periods of cosmic evolution.

"With our new findings, we may be able to access a period in the history of the universe very close to the Big Bang," team member Yann Mambrini of the Université Paris-Saclay in France said.

The team's research was published in November in Physical Review Letters.

In 1971, astronaut David Scott stood on the lunar surface, holding a hammer and a feather, and in the vacuum of the moon, he let them go. They struck the gray dust at the exact same time. It was a poetic nod to Galileo, who, centuries earlier, disproved the Aristotelian notion that heavy objects "want" to be on the ground more than light ones do.

This wasn't just a parlor trick for the cameras; it was a demonstration of the weak equivalence principle, which is the bedrock of general relativity. It states that all objects, regardless of their mass or internal composition, fall at the exact same rate in a gravitational field. When Einstein was building his masterpiece theory, he didn't try to explain why this happens. He simply assumed it was a fundamental rule and moved on.

But what if there's an astrophysical creature that refuses to play by the rules? What if we dropped something so exotic, it wasn't even on Einstein's radar? We need to talk about antimatter.

To understand the allure of falling antimatter, we have to look at the history of its discovery. In the 1920s, physicist Paul Dirac was trying to force two very different worlds — quantum mechanics (the rules of the very small) and special relativity (the rules of the very fast) — to play together.

Dirac found an equation that worked, but it had a quirk. Just as the square root of 4 can be both 2 and -2, his equation offered two solutions for the energy of a particle: one positive and one negative. This was a problem. Positive energy has a "ground floor" at zero, but negative energy is a basement of a basement with no bottom.

Dirac's solution was what became known as the "Dirac sea." He imagined outer space not as an empty vacuum but as a filled "ocean" of negative energy states. If you kick one of these invisible particles into the positive realm, you leave behind a hole. That hole behaves like a normal particle but with an opposite charge. It was the first time a particle was predicted by pure math before being seen in a lab. We call it antimatter.

Why focus on antimatter to test gravity? Because antimatter is the bridge to the greatest divide in physics. General relativity (gravity) and quantum mechanics (everything else) famously do not get along. They speak different languages and live in different neighborhoods. Because antimatter is a pure product of the quantum world, it is the perfect candidate to test Einstein's theory of gravity.

However, this is a nightmare, for three reasons:

1. When matter and antimatter touch, they annihilate in a flash of pure energy.
2. Nature doesn't just hand us antimatter; we have to build it in advanced laboratories.
3. Compared with the electromagnetic force, gravity is incredibly weak.

To overcome these hurdles, scientists at CERN's ALPHA-g experiment had to get creative. First, they made neutral antihydrogen by pairing antiprotons with positrons (anti-electrons). Because these antiatoms are neutral, they aren't pushed around by electricity.

The team caught about a hundred of these antiatoms in a Penning trap, which is a magnetic bottle that holds them in place because, while neutral, they still act like tiny bar magnets. Then, using lasers, the researchers chilled the atoms to near absolute zero to stop them from jiggling.

Then came the moment of truth: They slowly turned down the magnetic field.

If antimatter ignored the weak equivalence principle, the atoms might have drifted upward, repelled by Earth. If Einstein was right, they should tumble downward. The researchers waited for the flash of annihilation as the antiatoms escaped the trap and hit the walls of the container. After they filtered out the noise of stray cosmic rays, the results were clear: Roughly 80% of the antiatoms fell through the bottom of the trap.

Antimatter falls down. It's an anti-climactic (ha ha) result in the best way possible. It means the weak equivalence principle holds firm and Einstein's vision of a universal gravitational response remains unblemished.

However, the case isn't entirely closed. While we know antimatter falls down, we don't yet know if it falls at the exact same acceleration as regular matter does. If there is even a 1% difference in the speed of the fall, it would signal a total revolution in physics — a sign that gravity treats mirror matter differently. But for now, the universe remains a place where hammers, feathers and antihydrogen all race to the floor at the same speed.

If dark matter particles decay, then scientists could hunt for signs of this process, including X-ray or gamma-ray radiation or even emitted "ghost particle" neutrinos, in vast clusters of galaxies.

Not only could this finally reveal what particles comprise mysterious dark matter, but it could also help astronomers understand the universe's structure like never before. And new research suggests that NASA's X-ray Imaging and Spectroscopy Mission (XRISM) could play an important role in this hunt.

Dark matter poses a significant challenge for scientists because, despite comprising around 85% of the matter in the cosmos, it remains effectively invisible. This is because it doesn't interact with electromagnetic radiation, or light — or, if it does, the interaction is too weak to be detected. This has led scientists to suggest a whole host of hypothetical particles to account for dark matter, which go beyond the standard model of particle physics and the electrons, protons and neutrons that make up the atoms that compose all everyday matter, like stars, planets, moons and our bodies.

One particular dark matter model suggests that whatever particles make up this mysterious stuff, they undergo a process called decay. This involves large particles breaking down over vast timescales to lighter particles, releasing energy in the form of photons, the particles of light. One possible signature of this process that astronomers could hunt for are X-ray photons released when decay occurs. In fact, scientists may have already spotted this cosmic fingerprint in the form of an unidentified X-ray emission in the light spectra from galaxy clusters.

"Eighty-five percent of mass in galaxy clusters comes from dark matter, and we can model the dark matter radial distribution well," study team member Ming Sun, of the University of Alabama in Huntsville (UAH), said in a statement. "Thus, galaxy clusters are great targets for such a search as they are dark matter-rich and we know the dark matter mass in clusters well."

In the past, researchers have relied on light-sensitive semiconductor chips called Charge-Coupled Devices (CCDs) to track the paths of possible decay particles to better understand what is causing this X-ray emission. However, Sun and colleagues took a different approach, instead turning to data from XRISM.

"Nearly all the past studies used the CCD data, which lack the required energy resolution to resolve the unidentified line," Sun said. "Now XRISM provides high-energy-resolution spectra that can resolve the line. As the line signals are very weak, we combined nearly three months of the XRISM data for such a search. There are many X-ray lines detected. They originate from known atoms, such as iron, silicon, sulfur, and nickel. X-ray emission lines that appear that are not at the known position of atomic lines are then the candidates for dark matter decay lines, which is the focus of this work."

The team theorizes that the leading suspects for this unknown emission are "sterile neutrinos." Neutrinos are virtually massless particles that stream through the cosmos at nearly the speed of light. The second-most abundant particle in the universe after photons, neutrinos are so "ghost-like" that 100 trillion pass through your body every single second, and you never notice a thing. Sterile neutrinos are one of the hypothetical particles that have been proposed to account for dark matter.

"A sterile neutrino is a hypothetical type of neutrino that only interacts with other particles via gravity, unlike the three known 'active' neutrinos that also interact via the weak force," Sun said. "The existence of the sterile neutrino is well-motivated theoretically and can explain the very small but non-zero mass of regular neutrinos. Sterile neutrinos can decay into two photons with the same energy. Models can predict the decay rate of sterile neutrinos, which is then constrained from the data."

Sterile neutrinos have a long way to go before they replace Weakly Interacting Massive Particles (WIMPs) as the leading suspects for dark matter, but Sun and colleagues are committed to exploring other possible candidates, including sterile neutrinos, even if that process includes ruling them out.

"WIMPs are still the leading candidate for dark matter, but billions of dollars of experiments have been done, only getting stronger and stronger upper limits, so alternative scenarios have to be considered. This study provides the strongest limits from high-energy-resolution data on the sterile neutrino at the 5 to 30 kiloelectronvolts (keV) band, subsequently limiting the models for dark matter," the UAH researcher concluded. "With more XRISM data in the next five to 10 years or so, we will be able to either detect the line or improve the limit substantially."

The team's research was published in November in The Astrophysical Journal Letters.

New research puts forward compelling new evidence that dark matter interacts with cosmic "ghost particles" called neutrinos. If that is the case, then this interaction could pose a serious challenge for the standard model of cosmology, our current best model of the universe.

Neutrinos earn their spooky nickname due to the fact that as these chargeless and virtually massless particles travel through space at near the speed of light, they barely interact with other particles, ghosting their way through solid objects like planets. In fact, the interactions between these particles and other matter are so rare and fleeting that every second, around 100 trillion neutrinos stream through your body without you feeling a thing. Dark matter is similar; even though it accounts for around 85% of the matter in the universe, whatever comprises dark matter also barely interacts with ordinary matter and light, if at all. In fact, effectively invisible, dark matter can only be inferred due to its interaction with gravity and the effect this has on light and conventional matter.

However, new findings from a team of researchers from the University of Sheffield suggest that a slight interaction, in the form of a minor exchange of momentum, exists between dark matter and neutrinos. That contradicts the so-called "Lambda Cold Dark Matter (LCDM)" model that attempts to explain the universe's structure and evolution, which says that dark matter and neutrinos exist independently and do not interact with each other.

The evidence for this potentially paradigm-shift-inducing suggestion comes from observations of the universe in its current state, conducted by the Dark Energy Camera on the Victor M. Blanco Telescope in Chile, from galaxy maps created by the Sloan Digital Sky Survey, and details of the universe's distant past gathered by both the Atacama Cosmology Telescope (ACT) and the European Space Agency (ESA) Planck Telescope spacecraft.

These observations have revealed that the modern universe is less "clumpy" than it should be. This cosmic conundrum could be explained by interactions between dark matter and neutrinos, which would impact the way cosmic structures like galaxies form and evolve.

"Our results address a long-standing puzzle in cosmology. Measurements of the early universe predict that cosmic structures should have grown more strongly over time than what we observe today," team member Eleonora Di Valentino of the University of Sheffield said in a statement. “However, observations of the modern universe indicate that matter is slightly less clumped than expected, pointing to a mild mismatch between early- and late-time measurements. This tension does not mean the standard cosmological model is wrong, but it may suggest that it is incomplete.

"Our study shows that interactions between dark matter and neutrinos could help explain this difference, offering new insight into how structure formed in the universe," Di Valentino added.

The next step is to test this idea, something that the team thinks is possible using precise observations from future telescopes of a cosmic fossil called the Cosmic Microwave Background (CMB), a leftover from an event in the universe shortly after the Big Bang. Astronomers could also test this theory using a specific effect that objects of great mass have on space, and therefore light, a phenomenon called "gravitational lensing." This would allow them to better measure the distribution of ordinary matter and dark matter.

"If this interaction between dark matter and neutrinos is confirmed, it would be a fundamental breakthrough," team member William Giarè of the University of Hawaii, said. "It would not only shed new light on a persistent mismatch between different cosmological probes, but also provide particle physicists with a concrete direction, indicating which properties to look for in laboratory experiments to help finally unmask the true nature of dark matter."

The team's research was published on Jan. 2 in the journal Nature Astronomy.

Exotic, dark astrophysical objects may be hiding in interstellar space, and a new proposal outlines how to find them: stare really, really hard.

We don't know what dark matter is, even though we strongly suspect it exists. We see circumstantial evidence for it everywhere, from the rotation rates of galaxies to the growth of the largest structures in the cosmos. For decades, cosmologists have thought dark matter is some sort of exotic particle that was previously unknown to the Standard Model of particle physics. This strange particle would not interact with light, or really much of anything else, except through its gravitational influence.

But searches for these dark matter particles have come up empty so far, driving theorists to get more creative with their ideas.

It could be that dark matter isn't made of zillions of tiny particles flying through the universe. Instead, it could be composed of bunched-up collections of much larger objects. In particular, the researchers behind a new study, published in November 2025 in the open access server arXiv, investigated two kinds of exotic objects.

The first is known as a boson star. In this model, dark matter is made of an ultra-ultra-ultra light particle — potentially millions of times lighter than neutrinos, the lightest known particles. They would be so light that their quantum nature would make them appear more like waves at galactic scales than like individual particles. But these waves would sometimes bunch up and collect on themselves, pulling together with their own gravity, without collapsing.

Another possibility is called Q-balls. In this model, dark matter isn't a particle at all but rather a quantum field that soaks all of space and time. Due to a special property of this field, it could occasionally pinch off, creating gigantic, stable, lump-like balls that wander the cosmos like a floating piece of flour in gravy that hasn't been mixed well.

Both boson stars and Q-balls, which live under the more general heading of exotic astrophysical dark objects (EADOs), are difficult to detect. They're large — roughly star-size — but they do not emit light of their own, making them nearly invisible in our scans of the cosmos.

But astronomers have discovered a way that EADOs can betray their presence: microlensing. If a Q-ball or boson star were to pass between us and a distant star, the strong gravity of the EADO would cause the light from the star to act as a gravitational lens. From our perspective, it would make the star appear to suddenly jump into position and then quickly return to normal.

So all we'd have to do is stare at a whole bunch of stars for a really long time and hope we get lucky. Thankfully, we have just the instrument for the job. The Gaia space telescope's mission was to do just that: stare at a whole bunch of stars for a really long time.

The astronomers behind the study propose a campaign using Gaia data to search for Q-balls and boson stars by looking for their unique, "smoking gun" signal of sudden jumps in stellar positions. Depending on how many are out there, Gaia may have observed up to several thousand EADOs.

But if they're not out there, then this same campaign would produce stringent limits on Q-balls' and boson stars' contributions to the overall dark matter picture. No matter what, staring into the dark would teach us something.

Since it began operations in 2022, the James Webb Space Telescope (JWST) has allowed scientists to make incredible strides in our understanding of the cosmos  — especially its early epoch. However, one lingering cosmological mystery that the JWST hasn't had a major impact on is the nature of dark matter. Now, new research suggests that this is something that may soon change.

While dark matter is estimated to account for 85% of the matter in the universe, it is difficult to investigate because it doesn't interact with electromagnetic radiation (light) or it interacts so weakly that we can't directly detect it. As well as making dark matter effectively invisible, this lack of interaction with light tells scientists that the particles making up dark matter aren't the protons, neutrons, and electrons that comprise the everyday stuff we see around us on a day-to-day basis, ranging from the most massive stars to the viruses that make our lives miserable every winter. The search for a potential dark matter particle has delivered many suspects, but they've all remained frustratingly hypothetical.

Thus, the only way scientists can infer the presence of dark matter is by looking at the gravitational influence it has on the fabric of space and how this then impacts ordinary matter and light. This new research, published in the journal Nature Astronomy, suggests that the gravitational influence of dark matter may be the cause of strange young galaxies with unexpectedly elongated shapes. And investigating these shapes could reveal which of these hypothetical particles is the best recipe for dark matter.

Studying these elongated galaxies with the JWST might help reveal the presence of dark matter, scientists say. "In the expanding universe defined by Einstein’s theory of general relativity, galaxies grow over time from small clumps of dark matter that form the first star clusters and assemble into larger galaxies via their collective gravity," team member Rogier Windhorst, of Arizona State University, said in a statement.

"But now the JWST suggests that the earliest galaxies may be embedded in marked filamentary structures, which — unlike cold, dark matter — smoothly join the star-forming regions together, more akin to what is expected if dark matter is an ultralight particle that also shows quantum behavior."

Understanding dark matter is a stretch

When using simulations to recreate how the first galaxies formed in the early universe, allowing cool gas to gather along the threads in a web of dark matter is able to quite nicely recreate the mostly spheroid galaxies we see in the modern universe.

However, as the JWST has been allowing astronomers to look back at galaxies that existed in the very early stages of the universe, they have increasingly been finding filamentary elongated galaxies that aren't as easily recreated in simulations that stick to the standard mechanism of gas gathering to birth stars and grow galaxies.

To investigate this, Windhorst and colleagues looked at simulations of the universe involving different types of dark matter other than that found in the most accepted model of cosmology, the Lambda Cold Dark Matter (LCDM) model; "cold" dark matter, which doesn't refer to temperature but instead to the speed at which particles move.

This revealed that the wave-like behavior of "fuzzy dark matter" or ultralight axion particles could account for the elongated morphology of early galaxies seen by the JWST.

"If ultralight axion particles make up the dark matter, their quantum wave-like behavior would prevent physical scales smaller than a few light-years from forming for a while, contributing to the smooth filamentary behavior that JWST now sees at very large distances," team leader Álvaro Pozo of the Donostia International Physics Center said.

The team's modelling also indicated that faster-moving "warm dark matter" particles, like sterile neutrinos, could also give rise to early filamentary galaxies. In both the wave dark matter and warm dark matter scenarios, this is because these particles give rise to smoother filaments than cold dark matter. As gas and stars slowly flow down these filaments, elongated galaxies begin to form.

The JWST will continue to investigate oddly shaped galaxies in the early universe, while researchers here on Earth continue to evolve simulations of the early universe. Bringing these together could eventually help solve the mystery of dark matter.

The team's research was published on Dec. 8 in the journal Nature Astronomy.

This article was originally published at The Conversation. The publication contributed the article to Space.com's Expert Voices: Op-Ed & Insights.

Scientists working with the James Webb Space Telescope discovered three unusual astronomical objects in early 2025, which may be examples of dark stars. The concept of dark stars has existed for some time and could alter scientists' understanding of how ordinary stars form. However, their name is somewhat misleading.

"Dark stars" is one of those unfortunate names that, on the surface, does not accurately describe the objects it represents. Dark stars are not exactly stars, and they are certainly not dark.

Still, the name captures the essence of this phenomenon. The "dark" in the name refers not to how bright these objects are, but to the process that makes them shine — driven by a mysterious substance called dark matter. The sheer size of these objects makes it difficult to classify them as stars.

As a physicist, I've been fascinated by dark matter, and I've been trying to find a way to see its traces using particle accelerators. I'm curious whether dark stars could provide an alternative method to find dark matter.

What makes dark matter dark?

Dark matter, which makes up approximately 27% of the universe but cannot be directly observed, is a key idea behind the phenomenon of dark stars. Astrophysicists have studied this mysterious substance for nearly a century, yet we haven't seen any direct evidence of it besides its gravitational effects. So, what makes dark matter dark?

Humans primarily observe the universe by detecting electromagnetic waves emitted by or reflected off various objects. For instance, the moon is visible to the naked eye because it reflects sunlight. Atoms on the moon's surface absorb photons – the particles of light – sent from the sun, causing electrons within atoms to move and send some of that light toward us.

More advanced telescopes detect electromagnetic waves beyond the visible spectrum, such as ultraviolet, infrared or radio waves. They use the same principle: Electrically charged components of atoms react to these electromagnetic waves. But how can they detect a substance – dark matter – that not only has no electric charge but also has no electrically charged components?

Although scientists don't know the exact nature of dark matter, many models suggest that it is made up of electrically neutral particles – those without an electric charge. This trait makes it impossible to observe dark matter in the same way that we observe ordinary matter.

Dark matter is thought to be made of particles that are their own antiparticles. Antiparticles are the "mirror" versions of particles. They have the same mass but opposite electric charge and other properties. When a particle encounters its antiparticle, the two annihilate each other in a burst of energy.

If dark matter particles are their own antiparticles, they would annihilate upon colliding with each other, potentially releasing large amounts of energy. Scientists predict that this process plays a key role in the formation of dark stars, as long as the density of dark matter particles inside these stars is sufficiently high. The dark matter density determines how often dark matter particles encounter, and annihilate, each other. If the dark matter density inside dark stars is high, they would annihilate frequently.

What makes a dark star shine?

The concept of dark stars stems from a fundamental yet unresolved question in astrophysics: How do stars form? In the widely accepted view, clouds of primordial hydrogen and helium — the chemical elements formed in the first minutes after the Big Bang, approximately 13.8 billion years ago — collapsed under gravity. They heated up and initiated nuclear fusion, which formed heavier elements from the hydrogen and helium. This process led to the formation of the first generation of stars.

In the standard view of star formation, dark matter is seen as a passive element that merely exerts a gravitational pull on everything around it, including primordial hydrogen and helium. But what if dark matter had a more active role in the process? That’s exactly the question a group of astrophysicists raised in 2008.

In the dense environment of the early universe, dark matter particles would collide with, and annihilate, each other, releasing energy in the process. This energy could heat the hydrogen and helium gas, preventing it from further collapse and delaying, or even preventing, the typical ignition of nuclear fusion.

The outcome would be a starlike object — but one powered by dark matter heating instead of fusion. Unlike regular stars, these dark stars might live much longer because they would continue to shine as long as they attracted dark matter. This trait would make them distinct from ordinary stars, as their cooler temperature would result in lower emissions of various particles.

Can we observe dark stars?

Several unique characteristics help astronomers identify potential dark stars. First, these objects must be very old. As the universe expands, the frequency of light coming from objects far away from Earth decreases, shifting toward the infrared end of the electromagnetic spectrum, meaning it gets "redshifted." The oldest objects appear the most redshifted to observers.

Since dark stars form from primordial hydrogen and helium, they are expected to contain little to no heavier elements, such as oxygen. They would be very large and cooler on the surface, yet highly luminous because their size — and the surface area emitting light — compensates for their lower surface brightness.

They are also expected to be enormous, with radii of about tens of astronomical units — a cosmic distance measurement equal to the average distance between Earth and the sun. Some supermassive dark stars are theorized to reach masses of roughly 10,000 to 10 million times that of the sun, depending on how much dark matter and hydrogen or helium gas they can accumulate during their growth.

So, have astronomers observed dark stars? Possibly. Data from the James Webb Space Telescope has revealed some very high-redshift objects that seem brighter — and possibly more massive — than what scientists expect of typical early galaxies or stars. These results have led some researchers to propose that dark stars might explain these objects.

Dark stars may explain early black holes

What happens when a dark star runs out of dark matter? It depends on the size of the dark star. For the lightest dark stars, the depletion of dark matter would mean gravity compresses the remaining hydrogen, igniting nuclear fusion. In this case, the dark star would eventually become an ordinary star, so some stars may have begun as dark stars.

Supermassive dark stars are even more intriguing. At the end of their lifespan, a dead supermassive dark star would collapse directly into a black hole. This black hole could start the formation of a supermassive black hole, like the kind astronomers observe at the centers of galaxies, including our own Milky Way.

Dark stars might also explain how supermassive black holes formed in the early universe. They could shed light on some unique black holes observed by astronomers. For example, a black hole in the galaxy UHZ-1 has a mass approaching 10 million solar masses, and is very old – it formed just 500 million years after the Big Bang. Traditional models struggle to explain how such massive black holes could form so quickly.

The idea of dark stars is not universally accepted. These dark star candidates might still turn out just to be unusual galaxies. Some astrophysicists argue that matter accretion — a process in which massive objects pull in surrounding matter — alone can produce massive stars, and that studies using observations from the James Webb telescope cannot distinguish between massive ordinary stars and less dense, cooler dark stars.

Researchers emphasize that they will need more observational data and theoretical advancements to solve this mystery.

Scientists may have "seen" dark matter for the first time, thanks to NASA's Fermi gamma-ray space telescope. If so, this would mark the first direct detection of the universe's most mysterious substance.

Dark matter was theorized in 1933 by astronomer Fritz Zwicky, who found that the visible galaxies of the Coma Cluster lacked the necessary gravitational influence to prevent this cluster from flying apart. Then, in the 1970s, astronomer Vera Rubin and colleagues found the outer edges of spiral galaxies were spinning at the same rate as their centers, something that would only be possible if the major amount of mass in these galaxies wasn't concentrated at their centers, but rather more widely dispersed. These aren't direct observations of dark matter, of course, but inferences made using dark matter's interactions with gravity as well as the influence gravity then has on ordinary matter and light. Still, because of these findings, s astronomers have since calculated that all large galaxies are embedded within vast haloes of dark matter that expand way beyond the limits of visible matter in galaxies (such as galactic haloes of stars).

The particles of this mysterious substance are now estimated to outweigh the particles that make up everyday matter by a ratio of five to one. That means everything we see around us on a day-to-day basis — stars, planets, moons, our bodies, next door's cat, and so on — all account for just 15% of the matter in the universe, with dark matter accounting for the other 85%. Adding to the mystery of dark matter is the fact that, because it interacts with electromagnetic radiation so weakly, or not at all, it doesn't emit, absorb, or reflect light. Thus, it is effectively invisible in all wavelengths of light — or at least, we thought it was.

There is one possibility that would result in dark matter producing light. If dark matter particles "annihilate" when they meet each other and interact, much as matter and its counterpart antimatter do, then it should produce a shower of particles, including photons of gamma-rays that, while invisible to our eyes, could be "seen" by sensitive gamma-ray space telescopes. One of the suggested "self-annihilating" particles theorized to comprise dark matter are so-called "Weakly Interacting Massive Particles" or "WIMPS."

A team of researchers, led by Tomonori Totani from the Department of Astronomy at the University of Tokyo, trained the Fermi spacecraft on the regions of the Milky Way where dark matter should congregate, namely at the center of our galaxy, and hunted for this telltale gamma-ray signature.

Well, Totani thinks we finally found that signature.

"We detected gamma rays with a photon energy of 20 gigaelectronvolts (or 20 billion electronvolts, an extremely large amount of energy) extending in a halolike structure toward the center of the Milky Way galaxy," Totani said. "The gamma-ray emission component closely matches the shape expected from the dark matter halo."

And this isn't the only close match. The energy signature of these gamma-rays closely matches those predicted to emerge from the annihilation of colliding WIMPs, which are predicted to have a mass around 500 times that of a proton, the ordinary matter particles found at the heart of atoms. Totani suggests there aren't any other astronomical phenomena that easily explain the gamma-rays observed by Fermi.

"If this is correct, to the extent of my knowledge, it would mark the first time humanity has ‘seen’ dark matter. And it turns out that dark matter is a new particle not included in the current standard model of particle physics," Totani said. "This signifies a major development in astronomy and physics."

While Totani is confident that what he and his colleagues have detected is the signature of dark matter WIMPs annihilating each other at the heart of the Milky Way, the scientific community in general will require more hard evidence before the book is closed on this nearly century-old mystery.

"This may be achieved once more data is accumulated, and if so, it would provide even stronger evidence that the gamma rays originate from dark matter," Totani added.

The team's research was published on Tuesday (Nov. 25) in the Journal of Cosmology and Astroparticle Physics.

As if dark energy weren't already mysterious and baffling enough, new research suggests that this unknown force may not be driving galaxies apart at an accelerating rate anymore.

This remarkable result comes from research that suggests that the expansion of the universe has already begun to slow, contrary to the currently favored belief that dark energy is still accelerating the expansion of the cosmos. The discovery also follows results from the Dark Energy Spectroscopic Instrument (DESI) that last year indicated that dark energy is weakening.

This research could not only revolutionize our understanding of the universe as it is today, but also offer clues about how our cosmos will end. If dark energy has already lost the battle against gravity, the next step after slowing cosmic expansion could be the contraction of space, and that could suggest the universe will end in a "Big Crunch" scenario akin to the Big Bang playing in reverse.

The researchers behind this discovery are already hailing it as a possible paradigm shift in how we think about the very nature of the universe. "Our study shows that the universe has already entered a phase of decelerated expansion at the present epoch and that dark energy evolves with time much more rapidly than previously thought," Young-Wook Lee, team leader and researcher at Yonsei University in South Korea, said in a statement. "If these results are confirmed, it would mark a major paradigm shift in cosmology since the discovery of dark energy 27 years ago."

Dark energy evolves

The existence of dark energy was first suggested in 1998 when two separate teams of astronomers observed distant Type Ia supernovas, also referred to as "standard candles" due to the fact that their uniform light output can be used to measure cosmic distances. This revealed that the further away a galaxy was, the faster it was receding away. This indicated to the two teams, who received the 2011 Nobel Prize in Physics for the discovery, that the speed at which the universe expands is increasing. Dark energy was introduced as a placeholder force to explain this accelerating expansion.

Over the following three decades, while scientists have been unable to conclusively determine what dark energy is, they have found that this force is dominant, accounting for approximately 68% of the universe's total energy-matter budget. Researchers also discovered that dark energy had not always been dominant, appearing to begin its rule and start speeding up the expansion of the universe around 5 billion years ago, or roughly 9 billion years after the Big Bang.

The first indication that dark energy may not be as dominant as previously thought emerged courtesy of the first results from DESI in Spring 2024. This new chink in the armor of dark energy resulted from Lee and colleagues from Yonsei University discovering that Type Ia supernova may not be quite so standard after all. That is because their brightness may be strongly affected by the age of the progenitor stars of these explosive events. In fact, this team found that even after the light from Type Ia supernovas was standardized, Type Ia supernovas from populations of younger stars were fainter than those belonging to older stellar populations.

Using a sample of 300 galaxies, the research suggested a significance of 99.99% that the dimming of distant Type Ia supernovas can arise not just from cosmological effects like the expansion of space, but also from stellar effects. Correcting for bias, the team found that their results rule out the currently favored model of cosmic evolution, the standard model of cosmology, or the Lambda Cold Dark Matter (LCDM) model, and its recipe of dark energy.

However, the major result emerging from this research is the implication that the universe is not expanding at an accelerating rate, but has already transitioned into a state of decelerating expansion. That goes even further than DESI's hints at weakening dark energy.

"In the DESI project, the key results were obtained by combining uncorrected supernova data with baryonic acoustic oscillations measurements, leading to the conclusion that while the universe will decelerate in the future, it is still accelerating at present," Lee explained. "By contrast, our analysis — which applies the age-bias correction — shows that the universe has already entered a decelerating phase today."

The next step for the team will be to confirm these results by conducting an "evolution-free test" utilizing only young Type Ia supernovas from young galaxies at a range of distances. The Vera C. Rubin Observatory, which has just begun observing the cosmos with the world's largest digital camera from its position atop Cerro Pachón in Chile, is poised to play a major role in this investigation.

"Within the next five years, with the Vera C. Rubin Observatory discovering more than 20,000 new supernova host galaxies, precise age measurements will allow for a far more robust and definitive test of supernova cosmology," Chul Chung, team member and Yonsei University researcher, said.

The team's research was published on Wednesday (Nov. 5) in the journal Monthly Notices of the Royal Astronomical Society.

Scientists have discovered that dark matter, the universe's most mysterious "stuff," obeys gravity on vast cosmological scales. This could help to dismiss the possibility of a fifth fundamental force of nature — but even if not, it certainly puts restraints on that potential force's strength.

It's long been known that "everyday matter" is made up of atoms, which are, in turn, composed of protons, neutrons and electrons. We also know that these particles fall in line with the known fundamental forces of nature: electromagnetism, gravity, the strong nuclear force and the weak nuclear force. However, what has been less clear is whether dark matter obeys these same four forces. Indeed, one of the reasons dark matter is so puzzling is that it doesn't seem to act in conjunction with light, or electromagnetic radiation. And if it does, it does so much more weakly than ordinary matter does. This makes dark matter effectively invisible, meaning the only way scientists can infer its presence is by observing its gravitational effects and then watching how that acts as a middleman and impacts light and ordinary matter.

But determining that dark matter interacts gravitationally on relatively small scales, such as within galaxies, doesn't tell us if it obeys the well-understood laws of gravity as defined by Albert Einstein's 1915 theory of gravity, general relativity, on much larger cosmological scales. That is a big question because accounting for five times more of the matter in the universe than everyday matter, dark matter should have played a major role in how the cosmos developed.

To solve this conundrum and to discover if dark matter could be governed by a fifth, thus far unknown fundamental force, researchers from the University of Geneva (UNIGE) set about determining if dark matter falls into cosmic gravity wells on vast scales just as ordinary matter does. These gravity wells are created when bodies of tremendous mass cause the very fabric of space and time, unified as a single four-dimensional entity called "spacetime," to warp (as established by general relativity). The greater the mass of the body, the more extreme the warping of spacetime, the "deeper" the resultant gravity well, and thus the stronger the gravitational influence.

"To answer this question, we compared the velocities of galaxies across the universe with the depth of gravitational wells," Camille Bonvin, team member and UNIGE researcher, said in a statement. "If dark matter is not subject to a fifth force, then galaxies — which are mostly made of dark matter — will fall into these wells like ordinary matter, governed only by gravity.

"On the other hand, if a fifth force acts on dark matter, it will influence the motion of galaxies, which would then fall into the wells differently. By comparing the depth of the wells with the galaxies' velocities, we can therefore test for the presence of such a force."

With this approach and using up-to-date cosmological data, the team established that dark matter does indeed slip into gravity wells just as ordinary matter does. While these findings provide no hints of a fifth fundamental force of nature, they can't absolutely rule it out.

"At this stage, however, these conclusions do not yet rule out the presence of an unknown force. But if such a fifth force exists, it cannot exceed 7% of the strength of gravity — otherwise it would already have appeared in our analyses," Nastassia Grimm, team leader and researcher at the Institute of Cosmology and Gravitation, University of Portsmouth in the UK.

While these results don't close the book on a fifth force of nature governing dark matter, they do help better define the characteristics of this disturbingly elusive form of matter. And if there is a fifth force of nature, it likely won't be able to hide forever.

"Upcoming data from the newest experiments, such as LSST [the Legacy Survey of Space and Time conducted by the Vera C. Rubin Observatory and DESI [the Dark Energy Spectroscopic Instrument], will be sensitive to forces as weak as 2% of gravity," Isaac Tutusaus, team member and researcher at the University of Toulouse, said. "They should therefore allow us to learn even more about the behaviour of dark matter."

The team's research was published on Monday (Nov. 3) in the journal Nature Communications.

From galaxy rotation curves that defy Newton's laws to gravitational lensing that bends light in eerie ways, scientists have been piecing together clues about dark matter like interstellar sleuths.

Particle physicists, astronomers, and cosmologists have built massive underground detectors, launched satellites, and even proposed entire new particles — all in pursuit of this elusive substance.

This quiz will test your knowledge of the strange, shadowy realm of dark matter. We'll explore the history of its discovery, the theories that try to explain it, and the cutting-edge experiments designed to catch it in the act.

Whether you're a seasoned space nerd or just curious about the universe's biggest mystery, you're in for a brain-bending ride.

Try it out below and see how well you score!

The century-old mystery of dark matter — the invisible glue thought to hold galaxies together — just got a modern clue.

Scientists say they may be one step closer to confirming the existence of this elusive material, thanks to new simulations suggesting that a faint glow at the center of the Milky Way could be dark matter's long-sought signature.

"It's very hard to actually prove, but it does seem likely," Moorits Muru of the Leibniz Institute for Astrophysics Potsdam in Germany, who led the new study, told Space.com.

Dark matter, which makes up about 27% of the matter in the universe, remains one of the biggest riddles in cosmology. It doesn't absorb or reflect light, making it completely invisible to telescopes. Despite decades of experiments, from underground particle detectors to orbiting space observatories, scientists have never detected it directly. Now, however, new computer simulations from Muru's team may have brought us a step closer to decoding the mystery.

The findings, show that dark matter near the Milky Way's center might not form a perfect sphere as scientists long thought. Instead, it appears flattened, almost egg-shaped, and that shape closely mirrors the pattern of mysterious gamma rays observed by NASA's Fermi Gamma-ray Space Telescope.

This builds on research dating back to 2008, when Fermi first spotted a broad, hazy glow of high-energy light near the galactic core, stretching across some 7,000 light-years. The signal was far brighter than existing models could explain.

Some scientists proposed that these rays could be the by-product of invisible dark matter particles known as WIMPs (short for weakly interacting massive particles) colliding and annihilating one another. Others argued they came from fast-spinning stellar remnants known as millisecond pulsars — ancient, rapidly spinning neutron stars that emit beams of radiation like cosmic lighthouses.

The pulsar theory made sense because the gamma-ray glow appeared flattened and bulging, much like the Milky Way's star-filled central region. If dark matter were behind the glow, scientists had expected a smoother, rounder pattern.

Muru and his team decided to put both ideas to the test. Using powerful supercomputers, they recreated how the Milky Way formed, including billions of years of violent collisions and mergers with smaller galaxies. Those violent events, the researchers found, left deep "fingerprints" on the way dark matter is distributed in the galactic core.

When this complex history is factored in, the simulated dark matter halo no longer looks spherical. Instead, it takes on a flattened, egg-like form — matching the pattern of gamma-ray emission Fermi has observed, the new study reports.

"We're showing that dark matter also has this flattened shape," Muru said. "So, it does match the [gamma ray] excess much better than expected before."

The finding suggests that dark matter could still be a strong contender behind the Milky Way's mysterious glow. But it doesn't completely rule out pulsars, the researchers say. Both possibilities, the team concludes, are now "essentially indistinguishable."

If the excess truly arises from dark matter collisions, it would mark the first indirect evidence that WIMPs, a leading dark matter candidate, really exist.

Definitive answers could come by the late 2020s, when the Cherenkov Telescope Array Observatory (CTAO) begins scanning the skies from its twin sites in Chile and Spain. The facility will be able to observe gamma rays at much higher resolution than Fermi, researchers say, potentially helping them distinguish between a swarm of pulsars, which have higher energies, and lower-energy annihilating dark matter particles.

Muru added that gamma-ray observations of smaller dwarf galaxies orbiting the Milky Way, whose cores also host dark matter in dense pockets, could further test both possibilities.

"That's where we hope to measure the signal," said Muru. "We're really looking forward to these observations."

Scientists are convinced dark matter is out there. The quest to detect it arguably remains both one of the most frustrating and most exhilarating challenges in modern physics.

"For some reason, it still eludes us," Muru said. "And I think the mystery makes it even more interesting."

The results were detailed in a paper published Oct. 16 in the journal Physical Review Letters.

Astronomers have unveiled a new catalog of massive galaxy clusters, revealing insight on the evolution of the universe.

Galaxy clusters — the largest gravitationally bound structures in the universe — act as cosmic signposts that trace the distribution of dark matter and the mysterious dark energy driving the universe's accelerated expansion. Each containing hundreds to thousands of galaxies, these clusters' characteristics such as size depend on how cosmic structures form and evolve. Thus, they're a powerful test of cosmological models.

The new catalog of galaxy clusters was assembled using six years of data collected by the Dark Energy Survey (DES). The project leveraged a powerful Dark Energy Camera (DECam) mounted to the 4-meter Blanco Telescope in Chile to provide one of the most detailed looks yet at how matter clumps together across cosmic time, according to a statement from the University of Chicago.

Observations from the DES revealed tens of thousands of clusters spanning billions of light-years, giving scientists a vast dataset to measure how structure grows. The DES team used optical and near-infrared observations from the DECam to detect faint galaxies and estimate their distances, building a 3D picture of the cosmic web.

One of the main goals was to see whether the universe today behaves as predicted by the leading cosmological model, known as Lambda-Cold Dark Matter (LCDM). For years, scientists have debated a mild mismatch — the so-called "S8 tension" — between how strongly matter appears to clump in the present-day universe versus how it should based on early-universe data from the cosmic microwave background.

"Our results find that the Lambda-CDM model describes the observable universe well," Chun-Hao To, lead author of the study from the University of UChicago, said in the statement.

Because dark matter and dark energy cannot be observed directly, scientists use massive clusters to better understand these mysterious forces, which are known to push galaxies together or apart. And because clusters are so massive, it's easier to see the effects of dark matter and dark energy on them than it would be on smaller objects, the researchers said.

Creating the new catalog required careful modeling of how clusters overlap and how their masses are estimated. Future telescopes like the Vera C. Rubin Observatory and NASA’s Nancy Grace Roman Space Telescope will probe much deeper. As those observatories come online, astronomers expect to expand the catalog dramatically, tracking how clusters formed across more of the universe’s history.

For now, the new DES galaxy cluster catalog offers one of the clearest maps yet of the cosmic landscape. Their findings were published Sept. 18 in the journal Physical Review D.

Dark matter, one of the universe's best kept secrets, may have been quietly painting the cosmos in faint, detectable hues of red and blue all along, a new study suggests.

Dark matter makes up more than 80% of the matter in the universe, yet it doesn't emit, absorb, or reflect light, making it impossible to observe directly. Now, a new theoretical study by scientists at the University of York in the U.K. suggests light passing through dark-matter-rich regions of space could pick up a faint tint — slightly red or blue, depending on the kind of dark matter it encounters.

The effect would be extraordinarily subtle, far too weak for current telescopes to detect, but potentially measurable with the next generation of ultra-sensitive observatories, the researchers say.

"It's a fairly unusual question to ask in the scientific world, because most researchers would agree that dark matter is dark," study co-author Mikhail Bashkanov of the University of York said in a statement. "But we have shown that even dark matter that is the darkest kind imaginable — it could still have a kind of colour signature."

The team likens the concept to the "six handshakes rule," the 20th-century theory that any two people on Earth are connected by a chain of, at most, six acquaintances. In a similar way, the study suggests, even if dark matter doesn't interact directly with light, it might do so indirectly through intermediate particles that both sides "know," including the Higgs boson, the so-called "God particle" that represents the Higgs field, which is responsible for giving other particles their mass.

This indirect link could allow photons, the particles of light, to scatter ever so slightly off dark-matter particles, leaving behind a whisper of color or polarization "fingerprint" in the light, the study suggests.

"It's a fascinating idea, and what is even more exciting is that, under certain conditions, this 'colour' might actually be detectable," Bashkanov said in the statement. "With the right kind of next-generation telescopes, we could measure it."

In their study, published earlier this month in the journal Physics Letters B, Bashkanov and his team carried out what they say are the first detailed calculations of how strongly light could scatter off dark matter.

The findings suggest that if dark matter is made up of Weakly Interacting Massive Particles, or WIMPs, which interact through the weak nuclear force, then light passing through a WIMP-rich region would lose some of its high-energy blue photons first, leaving the transmitted light slightly red-tinted. In contrast, if dark matter interacts only through gravity, photons would scatter in the opposite way, giving the light a faint blue shift, the study notes.

In both situations, the interactions are minute but not zero, researchers say, meaning dark matter could leave behind a detectable "fingerprint" on light that travels through dense regions of it, such as the centers of galaxies or galaxy clusters.

Their calculations show that these effects could slightly distort the light spectrum of distant objects. A galaxy's glow, for instance, might appear microscopically redder or bluer depending on the dominant type of dark matter lying between it and Earth. In principle, such differences could help scientists distinguish between dark-matter models based on whether cosmic light skews red or blue as it travels through dark-matter-rich space.

"Right now, scientists are spending billions building different experiments — some to find WIMPs, others to look for axions or dark photons," Bashkanov said in the same statement. "Our results show we can narrow down where and how we should look in the sky, potentially saving time and helping to focus those efforts."

Detecting such tiny shifts would require ultra-precise telescopes and painstaking analysis of light that has traveled billions of light-years across the cosmos. Future observatories with exceptional spectral and polarization sensitivity, such as the European Extremely Large Telescope and NASA's Nancy Grace Roman Space Telescope, could one day test these predictions.

If confirmed, the findings would open an entirely new observational window on dark matter, bringing scientists a step closer to unraveling one of the greatest mysteries in cosmology.

A "dark object" detected as an anomalous notch in the arc of a gravitationally warped section of space, could be the smallest clump of pure dark matter yet found.

If so, it would further validate the concept of cold dark matter and will help constrain the properties of dark matter particles as physicists and astronomers continue to hunt for what exactly the invisible substance is made from.

"Hunting for dark objects that do not seem to emit any light is clearly challenging," said Devon Powell of the Max Planck Institute for Astrophysics in Germany in a statement.

The discovery came as a byproduct while scientists were observing an Einstein ring. This is the most spectacular form of gravitational lensing in which the gravity of a foreground object — in this case a massive elliptical galaxy — is warping space. The light from a background galaxy, almost perfectly aligned with the elliptical galaxy and our line of sight, is lensed into an almost complete ring around the foreground galaxy.

Combining the power of radio telescopes across the world, including the European Very Long Baseline Interferometric Network of radio telescopes in Europe, Asia, South Africa and Puerto Rico, plus the Green Bank Telescope in West Virginia in the U.S. and the Very Long Baseline Array in Hawaii, gave astronomers an instrument with a baseline almost as large as Earth.

The larger the baseline, the smaller the details that can be seen.

Astronomers led by John McKean of the University of Groningen, the University of Pretoria and the South African Radio Astronomy Observatory, and Devon Powell of the Max Planck Institute for Astrophysics in Germany, were aiming to resolve the lensed image of a compact symmetric object (CSO). This is an object, such as an active supermassive black hole, that is producing relatively small (smaller than 3,200 light-years) lobes of radio emission.

The team succeeded in identifying the CSO, but in doing so spotted something even more tantalizing. The data had to be analyzed with algorithms running on supercomputers that can produce a "gravitational image," which in essence maps where the gravity is. Close inspection of the gravitational image turned up something surprising: a notch in the arc of radio emission belonging to the CSO and its host galaxy. This notch can only be produced by another object between the background and foreground galaxies and with a mass a million times greater than our sun.

There are two explanations. One is that it is an inactive dwarf galaxy while the other, given that the object seems completely dark, is that it is a relatively small clump of dark matter: the smallest ever seen on its own, by a factor of 100, that's located 10 billion light-years away from us.

"Given the sensitivity of our data, we were expecting to find at least one dark object, so our discovery is consistent with the so-called cold dark matter theory on which much of our understanding of how galaxies form is based," Powell said. "Having found one, the question now is whether we can find more and whether the numbers will agree with the models."

Cold dark matter is the leading model of dark matter, which posits that it is made from low energy particles that can clump together through their mutual gravity. If dark matter were "hot," meaning high in energy, then it wouldn't be able to clump because all its particles would be speeding through space at almost the speed of light, like neutrinos do.

The question has always been, how small can clumps of cold dark matter become? And can small dark matter clumps exist without forming stars inside them? The size of the smallest dark matter clumps can therefore place constraints on the properties of dark matter particles.

"Finding low-mass objects such as this one is critical for learning about the nature of dark matter," said team-member Chris Fassnacht of the University of California, Davis.

The findings are described in two papers, one in Nature Astronomy discussing the dark object, and one in Monthly Notices of the Royal Astronomical Society focusing on the CSO.

This article was originally published at The Conversation. The publication contributed the article to Space.com's Expert Voices: Op-Ed & Insights.

For more than a century, physics has been built on two great theories. Einstein's general relativity explains gravity as the bending of space and time.

Quantum mechanics governs the world of particles and fields. Both work brilliantly in their own domains. But put them together and contradictions appear – especially when it comes to black holes, dark matter, dark energy and the origins of the cosmos.

My colleagues and I have been exploring a new way to bridge that divide. The idea is to treat information – not matter, not energy, not even spacetime itself – as the most fundamental ingredient of reality. We call this framework the quantum memory matrix (QMM).

At its core is a simple but powerful claim: spacetime is not smooth, but discrete – made of tiny "cells", which is what quantum mechanics suggests. Each cell can store a quantum imprint of every interaction, like the passage of a particle or even the influence of a force such as electromagnetism or nuclear interactions, that passes through. Each event leaves behind a tiny change in the local quantum state of the spacetime cell.

In other words, the universe does not just evolve. It remembers.

The story begins with the black hole information paradox. According to relativity, anything that falls into a black hole is gone forever. According to quantum theory, that is impossible. Information cannot be ever destroyed.

QMM offers a way out. As matter falls in, the surrounding spacetime cells record its imprint. When the black hole eventually evaporates, the information is not lost. It has already been written into spacetime's memory.

This mechanism is captured mathematically by what we call the imprint operator, a reversible rule that makes information conservation work out. At first, we applied this to gravity. But then we asked: what about the other forces of nature? It turns out they fit the same picture.

In our models assuming that spacetime cells exist, the strong and weak nuclear forces, which hold atomic nuclei together, also leave traces in spacetime. Later, we extended the framework to electromagnetism (although this paper is currently being peer reviewed). Even a simple electric field changes the memory state of spacetime cells.

Explaining dark matter and dark energy

That led us to a broader principle that we call the geometry-information duality. In this view, the shape of spacetime is influenced not just by mass and energy, as Einstein taught us, but also by how quantum information is distributed, especially through entanglement. Entanglement is a quantum feature in which two particles, for example, can be spookily connected, meaning that if you change the state of one, you automatically and immediately also change the other – even if it's light years away.

This shift in perspective has dramatic consequences. In one study, currently under peer review, we found that clumps of imprints behave just like dark matter, an unknown substance that makes up most of the matter in the universe. They cluster under gravity and explain the motion of galaxies – which appear to orbit at unexpectedly high speeds – without needing any exotic new particles.

In another, we showed how dark energy might emerge too. When spacetime cells are saturated, they cannot record new, independent information. Instead, they contribute to a residual energy of spacetime. Interestingly, this leftover contribution has the same mathematical form as the "cosmological constant", or dark energy, which is making the universe expand at an accelerated rate.

Its size matches the observed dark energy that drives cosmic acceleration. Together, these results suggest that dark matter and dark energy may be two sides of the same informational coin.

A cyclic universe?

But if spacetime has finite memory, what happens when it fills up? Our latest cosmological paper, accepted for publication in The Journal of Cosmology and Astroparticle Physics, points to a cyclic universe – being born and dying over and over. Each cycle of expansion and contraction deposits more entropy – a measure of disorder – into the ledger. When the bound is reached, the universe “bounces” into a new cycle.

Reaching the bound means spacetime's information capacity (entropy) is maxed out. At that point, contraction cannot continue smoothly. The equations show that instead of collapsing to a singularity, the stored entropy drives a reversal, leading to a new phase of expansion. This is what we describe as a "bounce".

By comparing the model to observational data, we estimate that the universe has already gone through three or four cycles of expansion and contraction, with fewer than ten remaining. After the remaining cycles are completed, the informational capacity of spacetime would be fully saturated. At that point, no further bounces occur. Instead, the universe would enter a final phase of slowing expansion.

That makes the true "informational age" of the cosmos about 62 billion years, not just the 13.8 billion years of our current expansion.

So far, this might sound purely theoretical. But we have already tested parts of QMM on today's quantum computers. We treated qubits, the basic units of quantum computers, as tiny spacetime cells. Using imprint and retrieval protocols based on the QMM equations, we recovered the original quantum states with over 90% accuracy.

This showed us two things. First, that the imprint operator works on real quantum systems. Second, it has practical benefits. By combining imprinting with conventional error-correction codes, we significantly reduced logical errors. That means QMM might not only explain the cosmos, but also help us build better quantum computers.

QMM reframes the universe as both a cosmic memory bank and a quantum computer. Every event, every force, every particle leaves an imprint that shapes the evolution of the cosmos. It ties together some of the deepest puzzles in physics, from the information paradox to dark matter and dark energy, from cosmic cycles to the arrow of time.

And it does so in a way that can already be simulated and tested in the lab. Whether QMM proves to be the final word or a stepping stone, it opens a startling possibility: the universe may not only be geometry and energy. It is also memory. And in that memory, every moment of cosmic history may still be written.

Are we living in a simulation? Well, the jury's out on that one. But humans do create simulations all the time.

In fact, the Euclid Consortium, the international group managing the European Space Agency's Euclid space telescope, just published the world's most extensive simulation of the universe. It maps an astonishing 3.4 billion galaxies and tracks the gravitational interactions of more than 4 trillion particles.

Called Flagship 2, the simulation draws from an algorithm designed by astrophysicist Joachim Stadel of the University of Zurich (UZH). In 2019, Stadel used the supercomputer Piz Daint — then the third most powerful supercomputer in the world — to run the calculation, ultimately creating an exceptionally detailed virtual model of the universe.

"These simulations are crucial for preparing the analysis of Euclid’s data," astrophysicist Julian Adamek of UZH, a collaborator on the project, said in a statement.

Since 2023, the Euclid space telescope has been mapping billions of galaxies across the universe, studying the distribution of dark energy and dark matter. The spacecraft will eventually scan about one-third of the night sky. Given the scale of the project, Euclid produces vast quantities of data — and simulations like Flagship 2 help speed up processing times.

While the team anticipates that Euclid's observations will closely match predictions from the simulation, there are likely surprises in store. Flagship 2 runs on the standard cosmological model, which is what we currently know about the universe's composition. But missions like Euclid are designed to challenge our current knowledge. "We already see indications of cracks in the standard model," Stadel said.

The team is particularly excited to study the mystery of dark energy, the force driving the expansion of the universe. As it stands in the standard cosmological model, dark energy is simply a constant. But Euclid's observations — which will look up to 10 billion years in the past — might reveal different characteristics. "We can see how the universe expanded at that time and measure whether this constant really remained constant," said Adamek.

Euclid's first observational data was released in March 2025, with the next publication of data sets scheduled for spring 2026.

Astronomers have discovered a rare cosmic alignment that reveals hidden dark matter, offering a new way to study the invisible substance that makes up most of the universe.

Data from the Northern Extended Millimeter Array (NOEMA) in the French Alps revealed an extra image in the center of what is known as an Einstein Cross — a gravitational lensing effect that causes light from a distant object to bend and appear as four distinct images arranged in a cross-like pattern. In recent observations, the light from a distant, dusty galaxy called HerS-3 was split into five rather than four images, suggesting something unusual was bending the light in this unexpected way, according to a statement from Rutgers University.

An Einstein Cross forms when the gravity of galaxies in the foreground bends and splits the light of a more distant galaxy into four distinct images. However, what puzzled astronomers with regard to the newly studied Einstein Cross this time was a curious fifth image sitting at the center of the cross.

At first, they suspected a data glitch, but the anomaly persisted in repeat observations, including data from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. The fifth image could not be explained by the visible foreground galaxies alone. Only after adding a massive, invisible halo of dark matter to their computer models could the researchers reproduce what the radio telescope had observed.

"We tried every reasonable configuration using just the visible galaxies, and none of them worked," Charles Keeton, co-author of the study and a professor at Rutgers, said in the statement. "The only way to make the math and the physics line up was to add a dark matter halo. That’s the power of modeling. It helps reveal what you can't see."

Dark matter cannot be seen directly, but its gravitational effects are evident throughout the cosmos. In this case, it not only created the rare lensing pattern but also magnified HerS-3, allowing astronomers to study the distant galaxy in greater detail and the effects of dark matter.

"This system is like a natural laboratory," Pierre Cox, lead author of the study and research director at the French National Centre for Scientific Research, said in the statement. "We can study both the distant galaxy and the invisible matter that’s bending its light."

The team's models suggest future observations could reveal additional features, such as gas flowing out of the galaxy, which would provide further evidence that dark matter is magnifying the details of HerS-3.

Their findings were published on Sept. 16 in The Astrophysical Journal.

Dark matter could be made from tiny black holes formed when so-called "dark baryons" collapse, scientists suggest. Or, alternatively, dark matter could be a type of particle created by a form of Hawking radiation on the cosmic horizon.

Here's what all that means.

Dark matter is the substance that appears to make up about 27% of our universe, compared to the 5% of our universe composed of "normal" matter. Scientists certainly know dark matter exists due to some peculiar effects observed in the cosmos that normal matter can't account for. However, nobody knows what dark matter is made of.

For decades, the leading candidate has been WIMPs, or Weakly Interacting Massive Particles. But as the search for WIMPs begins to falter with experiments continuing to turn up empty handed, new theories of dark matter are starting to surface. Among them are two new models developed by Stefano Profumo, who is a professor of theoretical physics at the University of California, San Diego — and his ideas take a very different view of the dark-matter problem.

"My attitude is that we've tried very hard to think about dark matter as a particle, but it hasn't worked out so far," Profumo told Space.com. "I think it's natural to take a break and look at the whole thing from a distance, and wonder whether we are fundamentally thinking about this in the wrong way."

In one paper, Profumo considers whether the "dark sector" could be what gives birth to dark matter. By dark sector, he isn't referring to how our universe is governed by dark matter and dark energy. Instead, he's referring to a kind of "mirror world" of particles that interact via forces that our world's kind of matter does not experience.

Profumo says the concept is not as strange as it may sound. For example, he highlights how the quarks inside protons and neutrons are bound together by the strong nuclear force.

"But then take electrons, which are absolutely blind to the strong force. They don't feel it at all. For them the strong force is a dark sector," said Profumo. "It's common in the Standard Model."

Dark baryons would be the equivalent of protons or neutrons in this dark sector, except that they could contain more than three quarks, Profumo says, and therefore be more massive.

The next step in the researcher's theory was inspired by his teenage son asking whether a sufficiently massive particle could collapse under its own gravity to form a mini black hole. The dark baryons in the dark sector, if it so exists, could be massive enough to do just that — and these tiny black holes could then be rife in the universe and collectively form what we call dark matter.

"I've worked with people who have thought very deeply about a dark-sector equivalent to the strong force, but they've never really pushed all the way to the black hole frontier," said Profumo. "But I really think it is a possibility that we need to take into consideration."

Black holes, large or small, are surrounded by an invisible boundary called the event horizon, inside which gravity is so strong that not even light can escape. However, the event horizon is 'hot' – particles created at the boundary by quantum effects can radiate away as what we call Hawking radiation (named for famous physicist Stephen Hawking, who is credited with the idea). Over time, Hawking radiation removes mass and energy from a black hole, causing it to gradually evaporate. For supermassive black holes, this would take an unimaginably long time — 10^100 years at least. However, black holes on the smallest scales — what we call the Planck scale —- can evaporate in an amount of time less than the age of the universe.

However, if we make certain assumptions about the nature of these black holes formed by the collapse of dark baryons, then their Hawking radiation could become suppressed, preventing them from evaporating and enabling them to act as dark matter.

Meanwhile, Profumo's other idea plays on the concept of Hawking radiation as well, but in a completely novel way.

We live in a universe that is expanding at an accelerating rate, taking regions of the cosmos so far away that their light will never reach us. This leads to a boundary, or a cosmic horizon, which defines the edge of the visible universe. There could be much more of the universe beyond this horizon, but we will never see it.

Now, let's go back in time to the moment of the Big Bang. The universe began with a burst of expansionist energy known as inflation. This inflationary period lasted a tiny fraction of a second. However, some models also posit that there was a second brief burst of expansionary energy that followed inflation.

"It is basically a period of mini-inflation," said Profumo. "It could be associated with inflation and how it ends, or it could be driven by a similar set-up to inflation."

This second expansionary period created cosmic horizons like the cosmic horizon that borders the visible universe today. However, the visible universe today is 93 billion light-years across, with Earth at its center (the concept of a "visible" universe is very observer dependent — observers in different parts of the cosmos will see a different volume of observable universe centered around themselves). The vast size of the visible universe means the temperature at the cosmic horizon is very low because space itself has become so spread out.

However, during the second burst of inflation, the universe was still incredibly compact and the temperature at the horizon was extremely hot.

Profumo realized these early cosmic horizons could act like event horizons; indeed, the concept is a bit like a black hole but turned inside-out because everything beyond the cosmic horizon is forever disconnected from us, just like everything inside a black hole's event horizon is separated from us. And just as Hawking radiation is emitted from a black hole's event horizon, Profumo suggests the cosmic horizon could also experience Hawking radiation in the same manner, and that the energy of this radiation could transform into some kind of dark matter particle.

"Maybe [dark matter] is as simple as that," said Profumo. "Early on, the universe behaved like a black hole, and there was stuff sprinkled into the universe because the universe was evaporating in the same way that a black hole evaporates."

This might seem somewhat arbitrary, because the location of the cosmic horizon depends upon the location of the observer. However, because the universe is homogenous (the same at every point on large scales) and isotropic (the same in all directions) — two truisms that we call the Cosmological Principle —- then any two observers should see the exact same amount of dark matter, wherever they are.

Profumo isn't necessarily saying dark matter has to be one of these two possibilities; indeed, the fact that he has developed two theories implies that he's reluctant to nail his colors to any particular mast.

"The aim of the game is to understand the breadth and scope of what dark matter could be, and to cast the net as wide as possible," said Profumo.

All we know for sure about dark matter is that it interacts via gravity, and yet despite its mystery it is utterly dominant in how matter in the universe assembles itself into galaxies. Almost a century since Fritz Zwicky first suggested the existence of dark matter, and about half a century since Vera Rubin confirmed the need for dark matter in our universe, we still don't know anything more about it. Experiments can narrow down dark matter's properties, so the more ideas we have on the table, the more likely it is that we will be able to match one of them up to the observed properties of dark matter.

Profumo's dark sector–black hole hypothesis was published on May 9 in Physical Review D, and his cosmic horizon model was published in the same journal on July 8.

On Monday (June 23), the public and the wider science community will get their first look at images from the Vera C. Rubin Observatory. This will arguably mark the biggest moment in astronomy since the first images from the James Webb Space Telescope (JWST) were revealed in the summer of 2022.

Rubin was built by the National Science Foundation and the U.S. Department of Energy's Office of Science on the mountain Cerro Pachón, high in the dry atmosphere of northern Chile. When its operational, the observatory will construct what Director of Rubin Observatory's construction, Željko Ivezić, described as the "greatest movie of all time and the most informative map of the night sky ever assembled."

The 8.4-meter telescope, equipped with the largest digital camera ever, will conduct the decade-long Legacy Survey of Space and Time (LSST), capturing the entire southern sky over Earth every 3 nights.

To get you properly prepped for the first images from Rubin, Space.com spoke to an array of scientists who will work with the observatory, as well as others who are just excited to see what images and data this groundbreaking instrument is set to reveal.

However, be warned: they're tight-lipped about just what images we will see.

"Until the images are revealed next week, all I can say is that people are going to be amazed at what we're able to see already," Andrés Alejandro Plazas Malagón, a researcher at Stanford University and part of the Rubin Observatory’s Community Science Team, told Space.com. "I am excited about using the largest digital camera in the world for astronomy — the LSSTCam, with 3.2 gigapixels — to survey the entire sky visible from its location in Chile over a 10-year period. This is something that has never been done before.

"We will be able to gather more data than any galaxy survey to date to help answer fundamental open questions in astronomy."

Mireia Montes: "It is going to be huge!"

Mireia Montes is a Ramón y Cajal Fellow at the Institute of Space Sciences (ICE-CSIC) who will use Rubin to track stars drifting between galaxies via the faint "intracluster light" they emit.

"Rubin is exciting because it is going to be huge! Surveys are normally limited by how much area they cover or how deep they go, following a method called the 'wedding cake strategy'," Montes said.

"This means they cover a large area but are not very detailed, or small areas in great detail. Large areas are good for having lots of galaxies, but depth is better for seeing faint things like the details of galaxies or very distant galaxies. You usually choose whether to go for depth or area. Rubin is going to provide both depth and area! This will help us to see things that are not usually very clear.

"The general public will see that the night sky is not as dark as we see it. In fact, when you look at deep images, you can see that there are objects (like stars and galaxies) everywhere you look. I think people are going to be amazed by the number of objects in this image, just as we were by the Hubble Deep Field ... but on a very different scale, as Rubin's camera is huge.

Rubin is going to show us the universe in a totally new way!"

Rubin and the dark universe

The wide-field view of Rubin will see the LSST gather data that could finally solve lingering mysteries surrounding dark energy, the force that accounts for around 68% of our universe's matter-energy content and causes the expansion of the cosmos to accelerate.

It is somewhat startling to consider that despite all of humanity's advances in science, we still only know what around 5% of the universe's contents are. All stars, planets, moons, animals, plants, and inanimate objects, everything we see is "baryonic matter" composed of atoms, but there is a lot more to the universe than this. The rest of the matter-energy content is known as the "dark universe."

Rubin has the right stuff to shine a light on the dark universe, which is divided into dark energy and dark matter, both of which account for about 17% of the universe's matter and energy but remains invisible because it doesn't interact with light.

"Studies of dark energy and dark matter are highly complementary with the Rubin Observatory and its LSST," Plazas Malagón said. "For dark energy, the LSST will measure the shapes and properties of billions of galaxies — an order of magnitude more than current photometric galaxy surveys — across cosmic time.

"This will allow Rubin to probe the growth of the large-scale structure of the universe, namely the cosmic web, which is dominated by dark matter, and the expansion history of the universe."

Plazas Malagón explained that the LSST will revolutionize the study of dark matter by mapping the sky with unprecedented depth and precision.

This will enable the detection of the smallest dark matter halos that surround small satellite dwarf galaxies and wrap around stellar streams. The observatory will also use a phenomenon first predicted in 1916 by Einstein called "gravitational lensing" to investigate the distribution of dark matter through large galaxies.

"It will test dark matter properties such as self-interactions, warm or ultra-light masses, and the presence of compact objects like primordial black holes," Plazas Malagón continued. "The LSST will also constrain exotic dark matter models — including axion-like particles — through stellar population measurements, and provide high-resolution maps of large-scale structure to explore how dark matter and dark energy interact.

"Combined with other experiments, LSST will offer powerful, complementary tests of dark matter's fundamental nature."

Among the most curious dark energy findings since its discovery in 1998 are hints from the Dark Energy Spectroscopic Instrument (DESI) that this mysterious force is weakening over time. The wide-field view of Rubin could help confirm this, which would prompt revisions to the standard model of cosmology, or Lambda Cold Dark Matter (LCDM), a model built on a constant dark energy strength.

"The LSST will collect vastly more data, which will help determine whether this is a real effect or just a fluctuation," Plazas Malagón explained. "In addition to studying dark energy, LSST will allow us to test the standard model of cosmology in other ways—examining the cold dark matter and dark energy hypotheses in the context of alternative models, including modified theories of gravity."

Luz Angela García Peñaloza: "An incredible milestone"

Luz Ángela García Peñaloza is a cosmologist in Bogotá, Colombia, specializing in dark energy. She explained why she is so excited about Rubin, its first images, and its ongoing mission.

"Rubin's first image release is an incredible milestone for the astronomical community. This observatory will cover the largest patch of the sky ever, capturing the light of approximately 20 billion galaxies.

Rubin (or LSST) is not only an impressive telescope that will complement the cosmic cartography we are doing with other galaxy surveys, but also a fantastic piece of engineering that will be online for the next 10 years.

We don't know yet what kind of images they will release on Monday, but I'm looking forward to seeing a deep field with tens of thousands of galaxies and stars. Remarkably, Vera Rubin is going to observe many, many galaxies in one night; thus, I expect to see beautiful images of the sky.

Rubin will help us constrain the Large Scale Structure of the universe and, along the same lines, the nature and dynamics of dark energy."

Rubin tracks stellar exiles, failed stars, supernovas and more

While Rubin will excel at studying galaxies en masse, some scientists will be interested in using its detailed view to look at what lies between those galaxies, namely, faint intracuster light.

"These processes are linked to the formation of clusters of galaxies, which are the largest structures bound by gravity in the universe," Mireia Montes is a Ramón y Cajal Fellow at the Institute of Space Sciences (ICE-CSIC), told Space.com. "Our understanding of the processes that form intracluster light is limited by small datasets. With Rubin, however, we will finally have the depth and numbers required to understand this light much better."

Montes added that the filters employed by Rubin will enable astronomers to determine the type of stars between galaxies that give rise to intracluster light.

That should then lead to the revelation of the origins of these "orphan" stars and how they came to drift between galaxies.

Rubin may also excel in spotting another type of faint stellar outcast, so-called "failed stars" or brown dwarfs. These are bodies that form like stars from a collapsing cloud of gas and dust, but fail to gather enough mass to trigger the nuclear fusion of hydrogen to helium in their cores, the process that defines what a main sequence star is.

The infrared vision of Rubin's Simonyi Survey Telescope combined with its wide field of view and ability to see deep into space, will make it the perfect instrument for discovering faint, infrared-emitting objects like brown dwarfs.

In fact, researchers have predicted that Rubin could detect thousands of brown dwarfs in the Milky Way, increasing our catalog of these "failed stars" by 20 times.

That could help us better understand the mass limit at which a star "succeeds" and becomes a star rather than a brown dwarf, and thus how our galaxy took shape.

Giuseppe Donatiello: "We must have an open mind to anything!"

Giuseppe Donatiello is an amateur astronomer from Italy who, thus far, has discovered a staggering 11 new dwarf galaxies in the local neighborhood of the Milky Way.

"Thanks to deep surveys, important discoveries have come in the Local Group, in particular, bizarre and decidedly unconventional objects have emerged. Rubin will certainly bring other similar discoveries, pushing their detection further," Donatiello said.

"The ability to go very deep will allow us to better define the timing in cosmic evolution, from the first stars to the current galaxies. Having such an instrument at our disposal does not limit the possibilities of observation, and we must have an open mind to anything new.

"Nature is more imaginative than we are!"

The future of astronomy is bright

This cursory list above is far from the extent of the phenomena that will be investigated by Rubin as it conducts the LSST.

"There will be major improvements in almost every area of astronomy," Montes said. "Understanding better our own Milky Way, the evolution of galaxies, finding more low-mass galaxies that will allow us to understand better how galaxy formation occurs at those masses, mapping the mass of our universe, and therefore understanding better our universe."

Plazas Malagón added that some of the other key questions the groundbreaking observatory could answer include: Are there undiscovered planets in the outer solar system (e.g., Planet Nine or Planet X)? What explosive and transient events occur in the universe? How do stars evolve and die? What are the electromagnetic counterparts to gravitational wave and neutrino events? What is the structure of the Milky Way's halo, disk, and bulge? What is the local galactic neighborhood like? Are there hazardous asteroids or comets that could impact Earth?

Phew! Little wonder scientists (and Space.com) are excited!

"I'm thrilled to see what the scientific community will do with this data," Alejandro Plazas concluded. "I'm especially excited about the new questions that will emerge — questions we haven't even imagined yet. We've built a discovery machine, and that's incredibly exciting to me.

"One of the most exciting aspects is the unexpected discoveries that lie ahead!"

At the very largest scales, galaxies are not scattered around randomly. Instead, they form a pattern called the cosmic web. In fact, this is the largest pattern found in nature, with galaxies clumping together to form clusters, stringing themselves along filaments that stretch tens of millions of light-years on a side, and extending along broad walls that separate vast regions of the universe from each other.

These are the cosmic voids. The smallest voids are about 20 million light-years across on a side, and the largest ones go for hundreds of millions of light-years. They are the true cosmic deserts. But just like deserts on Earth, they're not entirely empty. So what's in these cosmic voids?

Within the voids, sophisticated observations can detect faint hints of structures, like small, dim dwarf galaxies dotting the vast expanses. Computer simulations reveal that there is even more to the story.

In addition to normal matter, there's dark matter. We can only see high-density clumps of dark matter because those have enough gravity to pull in normal matter that turns into stars and galaxies to illuminate our observations. And in the voids, there simply isn't enough density of dark matter, so nothing really lights up.

But computer simulations show that there are filaments and tendrils of dark matter crisscrossing the voids like a faint echo of the grand cosmic web, repeating itself in miniature.

Yet there are regions deep within the cosmic voids where not even dark matter penetrates. These are the lowest-density regions of the entire universe.

Still, if you work hard enough and are patient enough, you will detect an occasional bit of matter. The overall average density of the universe is roughly one hydrogen atom per cubic meter, and in the deepest corners of the voids, the average density is over 100 times less than that. So you could swim through the deepest voids and encounter a single hydrogen atom in, say, an entire football field's worth of space.

There is something else that fills up the voids: radiation. The cosmic microwave background — the leftover light from when the universe was only 380,000 years old — soaks the entire cosmos, filling every cubic centimeter. It makes up the vast majority of the radiation in the universe. No matter where you go, you can't escape the cosmic microwave background.

But that radiation is very old and very deeply redshifted into the microwave bands. It carries essentially no energy, so it barely counts.

That leaves one other component of the deepest parts of the voids. It's a very weak component, but it is a critical one for the universe: dark energy. Dark energy accounts for roughly 70% of the total energy density of the cosmos, but in most of the dense structures, like galaxies and clusters, you never know it's there.

Deep in the voids, however, dark energy takes over. It's the only thing left. This means that although the voids lack matter, they are filled to the brim with dark energy. And it's in the voids that dark energy is doing its work of tearing the universe apart.

Structures known as "zippers" and "twisters" in the early universe may explain why dwarf galaxies tend to line up with each other, as well as hint at how dark matter operates in the universe.

Every major galaxy like the Milky Way has a retinue of smaller dwarf galaxies orbiting it. The Milky Way has several dozen, including the famous Large and Small Magellanic clouds. Beginning in the 1970s, astronomers noticed that these dwarf galaxies' positions and orbits weren't entirely random. Instead, dwarf galaxies tended to exist within the same plane. For example, the 11 brightest satellites of the Milky Way share a plane, and many dwarf galaxies around the Andromeda galaxy form what is known as the Great Plane of Andromeda.

When confronted with an observational mystery like this, astronomers turn to computer simulations to try to understand what's going on. That's because we can see only a small fraction of all the matter in the cosmos — just the matter that emits light. The vast majority of the mass of every galaxy, both big and small, is in the form of mysterious, invisible dark matter.

We can't directly observe dark matter, so we must use the simulations to piece together what that major component is doing and how it affects the visible galaxies. But computer simulations have routinely found that dwarf galaxies are just scattered everywhere, rather than being arranged into particular planes.

Because alignments of dwarf galaxies appear to be common, the theory of galaxy formation is at odds with observations. In a paper submitted to The Astrophysical Journal in April, a team of researchers led by Janvi Madhani at Johns Hopkins University dug deeper into sophisticated simulations to see if they could crack the mystery.

The team studied the evolution of 12 simulated galaxies that were similar to the Milky Way, following the flows of dark matter and gas over billions of years. Galaxies do not spring up in an instant. Instead, they grow over time as filaments of matter pour onto them, like a giant cosmic umbilical cord.

And it's in these filaments that the researchers found how dwarf galaxies can align with each other. Previous research assumed that once dwarf galaxies formed, they would scatter into random orbits. But the new simulations followed the evolution of the gas to much greater resolution and precision, which allowed the researchers to forget assumptions and see what was actually happening.

Related: The faintest star system orbiting our Milky Way may be dominated by dark matter

The new study found that instead of scattering, the filaments can lock in with each other and enhance themselves. When they do this, they keep the dwarf galaxies confined to a single plane.

But the orientation of that plane depends on what happens to the filaments as new streams of gas connect to the same host galaxy. Sometimes, the filaments enhance each other, in what the researchers call a "zipper" — like the zipper merge you perform on a highway on-ramp. This creates a plane of gas that eventually evolves into a collection of dwarf galaxies.

Another case involves a "twister," which is when a new filament merges with an existing one with a lot of angular momentum. This shifts the position of the plane but otherwise keeps it intact.

But if too many filaments connect to the same galaxy, then any pattern is destroyed and dwarf galaxies get random orbits.

Overall, the researchers found that we should expect planes of dwarf galaxies in roughly half — and perhaps up to 70% — of galaxies like the Milky Way and Andromeda.

Based on this work, there doesn't appear to be any great tension between what we expect dark matter and gas to do when they build galaxies and what actually happens. So, although it doesn't reveal a crack in our understanding of cosmology, it does solve a decades-long problem in astronomy.

Astronomers are especially interested in galaxy formation, especially in the early universe. Recently, the James Webb Space Telescope revealed rather mature galaxies appearing at surprisingly early times. Those galaxies could point the way to a new cosmological paradigm, or they might just be the result of a different kind of zipper-and-twister dance. Only more observations and better simulations will tell us.

A new model of the cosmos does away with the universe's two most troubling and mysterious elements, dark energy and dark matter, collectively referred to as the dark universe. Here's the idea.

The new concept replaces the dark universe with a multitude of step-like bursts called "transient temporal singularities" that erupt throughout the entire cosmos.

It's possible, scientists say, that these transient temporal singularities could open to flood the universe with matter and energy, causing the very fabric of space to expand. Those rifts would close so quickly they would remain undetectable, leaving us to see the expansion of the cosmos we credit to dark energy, and the gravitational influence we attribute to dark matter.

"The new model can account for both structure formation and stability, and the key observational properties of the expansion of the universe at large, by enlisting density singularities in time that uniformly affect all space to replace conventional dark matter and dark energy," research author Richard Lieu, a physics professor at The University of Alabama in Huntsville, said in a statement.

The dark universe under pressure

The dark universe is poses such a huge conundrum for scientists because it suggests that only 5% of the matter and energy in the cosmos comprises what we see around us on a day-to-day basis in stars, planets, moons, our bodies — and everything else, really.

In other words, we have no idea what the other 95% of the cosmos is.

Of this enormous slice of the universe's matter and energy budget, dark energy — the placeholder name for the force causing the expansion of the universe to accelerate — accounts for around 70%.

Dark matter, on the other hand, helped the first galaxies gather through its gravitational influence — but it remains effectively invisible because it doesn't interact with light. Yet, dark matter accounts for the remaining around 25% of that matter budget.

The ubiquity of dark matter and dark energy and their importance in our models of cosmic evolution make the dark universe a double mystery that scientists would love to resolve.

Building upon prior research in which he suggested that gravity could exist without the presence of mass, Lieu does away with the need for dark matter and dark energy.

Unlike previous attempts, however, Lieu's model doesn't need an exotic addition to current cosmological models, such as "negative mass" or "negative density," to negate the dark universe.

"Sir Fred Hoyle opposed Big Bang cosmology and postulated a 'steady state' model of the universe in which matter and energy were constantly being created as the universe expands," Lieu explained. "But that hypothesis violates the law of mass-energy conservation."

Lieu instead suggests that via transient temporal singularities, matter and energy can appear and disappear in sudden bursts. This doesn't violate the current conservation laws of physics.

"These singularities are unobservable because they occur rarely in time and are unresolvedly fast, and that could be the reason why dark matter and dark energy have not been found," Lieu added. "The origin of these temporal singularities is unknown – safe to say that the same is true of the moment of the Big Bang itself."

Lieu's model sees these singularities as generating a "negative pressure" with an anti-gravity-like effect serving to push the universe apart at an accelerating rate, just as dark energy is proposed to do.

"An example is the negative pressure exerted by a magnetic field along a field line," Lieu said. "Einstein also postulated negative pressure in his 1917 paper on the Cosmological Constant. When positive mass-energy density is combined with negative pressure, there are some restrictions which ensure the mass-energy density remains positive with respect to any uniformly moving observer, so the negative density assumption is avoided in the new model."

Lieu's ultimate conclusion is that the dark universe and its constituents may not be an omnipresent factor in the cosmos.

"They only appear in brief instances during which the matter and energy do fill the entire universe uniformly, apart from random spatial density variations which grow to form bound structures like galaxies," he continued. "In between which, they are not to be found anywhere.

"The only difference between this work and the standard model is that the temporal singularity occurred only once in the latter, but more than once in the former."

In the future, Lieu intends to try validating his theory by turning to ground-based telescopes to look for "jumps" in redshift — in reference to the stretching of light coming from distant objects as they recede away from us due to the expansion of space.

"The best way to look for the proposed effect is actually to use a large ground-based telescope – like the Keck Observatory [located in Hawaii], or the Isaac Newton Group of Telescopes in La Palma, Spain – to perform deep field observations, the data of which would be ‘sliced’ according to redshift,” he said. “Given sufficient redshift (or, equivalently, time) resolution effected by the redshift slicing, one might just find that the Hubble diagram exhibits jumps in the redshift distance relation, which would be very revealing."

Lieu's research was published on March 21 in the journal Classical and Quantum Gravity.

The latest wide-scale analysis of data from the Euclid Space Telescope has demonstrated just how big of an impact this European Space Agency (ESA) spacecraft is set to have on science. Importantly, it also shows that in science, sometimes good things come in small packages.

The space telescope — dubbed the "dark universe detective" due to its mission to better understand dark matter and dark energy — has been building the most extensive 3D map of the cosmos ever constructed.

Now, astronomers led by researchers from the University of Innsbruck have peered between the billions of stars, galaxies and supermassive black hole-powered quasars contained within 25 Euclid images to discover and characterize a staggering 2,674 dwarf galaxies.

"We took advantage of the unprecedented depth, spatial resolution, and field of view of the Euclid data," team leader Francine Marleau of the University of Innsbruck said in a statement. "This work highlights Euclid's remarkable ability to detect and characterize dwarf galaxies, enabling a comprehensive view of galaxy formation and evolution across diverse mass scales, distances and environments."

Dwarf galaxies come in many guises

Dwarf galaxies are tiny galaxies that contain up to a few billion stars rather than hundreds of billions of stars like their larger counterparts. These galaxies are also often seen orbiting larger galaxies. The Milky Way has numerous dwarf galaxy satellites of its own, for instance, the most famous of which are known as the Large Magellanic Cloud and the Small Magellanic Cloud.

It is believed that dwarf galaxies are created in the early stages of the development of large galaxies, or when collisions between two larger galaxies cause streams of material, including stars, gas, dust and dark matter, to be ejected into space.

Dwarf galaxies come in an array of different shapes. On one hand you have spheroid dwarf galaxies, spiral dwarf galaxies and elliptical dwarf galaxies, and on the other you have irregular dwarf galaxies. The latter are chaotic galaxies that lack a distinct shape, and are low in elements heavier than hydrogen and helium — akin to galaxies from the early universe. That makes dwarf irregulars good proxies for studying galaxies in the infant cosmos.

Altogether, the study and characterization of dwarf galaxies is important for understanding the evolution of galaxies. However, this isn't as easy as it sounds. The low stellar content of dwarf galaxies makes them faint and difficult to observe.

But that's why this massive Euclid haul of dwarf galaxies is such a big deal.

In fact, Marleau and colleagues were able to go beyond merely identifying dwarf galaxy candidates. They were also able to characterize many of these small conglomerations of stars and determine the distance to these galaxies, as well as assess their stellar masses and the type of environments they dwell in.

Of the galaxies identified, the team said 58% are elliptical dwarf galaxies and 42% are irregular dwarf galaxies. They found that just 1% of the dwarf galaxies observed by Euclid for this study are rich in globular clusters, which are tightly bound, nearly spherical collections of stars that usually contain the oldest stars found in a galaxy.

Around 4% of the identified dwarf galaxies contained a galactic nucleus, a dense central region packed with stars orbiting a small, dense and massive object (usually a black hole.).

Almost 7% of the dwarf galaxies were Blue Compact Dwarfs, which are small, irregular galaxies characterized by a high rate of star formation. This starburst activity results in a blue-colored, compact center, the coloration of which is due to young, hot massive stars.

Marleau and colleagues will now continue to use Euclid, which launched in July 2023, to discover and catalog more dwarf galaxies.

A pre-peer-reviewed version of the team's research is available on the paper repository site arXiv.

Hidden information in maps of galaxies spread across the universe could soon come forth, thanks to a new way of interrogating the data that preserves the three-dimensional nature of these maps.

The hidden information could be vital in telling us whether the standard model of cosmology is correct, or whether there are deviations from it that could affect our understanding of the "dark universe," which comprises dark matter and dark energy.

The research, led by astronomer Minh Nguyen of the University of Tokyo, utilizes powerful computer algorithms that are able to compare the relative positions of galaxies in a 3D map of the universe with detailed simulations that depict the growth and behavior of galaxies and haloes of dark matter.

Back in the old days, astronomers would conduct galaxy surveys by taking deep space images on photographic plates and then measuring directly on the plates, in two-dimensions, the spatial distribution of the galaxies. They'd try answering questions like "How close are these galaxies to their neighbors?" and "How well-aligned are they with one another?"

In modern times, a third dimension can be added to these surveys. It's all thanks to multi-object spectroscopy, which measures the redshift of these galaxies, and hence the distance to them in an expanding universe, in an observed volume of space. With such galactic distance measurements, it's actually possible to create a three-dimensional map of the universe.

However, the calculating power required to statistically analyze this three-dimensional galaxy data is fiendish, and so, for efficiency, the 3D data has traditionally been compressed down into what are called "n-point correlation functions," the "n" referring to a number (usually two or three points of data as mentioned above).

That's all well and good in most cases, but there has also been a nagging suspicion that compressing and analyzing the data this way results in information being missed — or hidden. And now, using a technique called "field-level inference" (FLI) in combination with a suite of algorithms in a framework called "LEFTfield" that models galaxy growth and clustering from the early universe to the present day, Nguyen's team has shown that vital information is indeed being suppressed by the compression. The team won third place in the Buchalter Cosmology Prize for this result.

"In field-level inference, we work directly with a 3D map of galaxies," Nguyen told Space.com. The map is represented on the computer by voxels, which are like three-dimensional pixels in a lattice grid. The FLI then depicts in this voxel lattice what it predicts the 3D structure of galaxies and underlying dark matter should look like according to the standard model of cosmology (which describes how large-scale structure in the universe evolves under the influence of dark matter and dark energy).

"With the help of powerful computer algorithms, FLI aims to match those predictions with the observed galaxy position at every point on the 3D lattice," said Nguyen.

N-point functions are popular because they speed up processing time and are more efficient to use, but today's algorithms are sophisticated enough to bridge the gap and enable the full, uncompressed data to be analyzed.

"Fortunately, there are modern computer algorithms that can speed up the exploration, or sampling, of this vast parameter space," said Nguyen.

Nguyen and his colleagues — Fabian Schmidt, Beatriz Tucci, Martin Reinecke and Andrija Kostić of the Max Planck Institute for Astrophysics in Germany — initially tested FLI on simulated maps of dark matter haloes, which are vast clouds of dark matter that surround galaxies and galaxy clusters. Think of the haloes as the scaffolding inside which visible matter assembles into galaxies. More recently, as part of "Beyond Two-Point Collaboration," Nguyen and Schmidt applied FLI on simulated galaxies as well, with the results soon to be published in The Astrophysical Journal Supplement Series.

Their results show a factor of between three and five improvement in detail and accuracy in the FLI analysis compared to two- and three-point correlation functions. This extra detail indicates that there is information that is being hidden in the old way of doing things.

And what can this hitherto hidden information tell us? Large-scale structures in the universe — the great chains of galaxy clusters that span the cosmos — can be traced back to the quantum fluctuations in the big bang that led to over-densities that grew under gravity into galaxies. FLI could reveal asymmetries in these fluctuations that have become frozen in time in the form of the distribution of galaxies, or how anomalies in the gravitational evolution of galaxies in the more recent universe could reveal details about dark matter, or in fact gravity itself.

In addition, "By having access to the entire underlying field of dark matter associated with the observed galaxy field, we might be more sensitive to local effects," said Nguyen. "Such local effects are averaged-over in analyses using n-point functions."

The next step is to put FLI to the test with real data from the Dark Energy Spectroscopic Instrument at Kitt Peak National Observatory, the Subaru Prime Focus Spectrograph and the European Space Agency's Euclid mission, and in the future the Vera C. Rubin Observatory that should see first light later this year in Chile, as well as the Nancy Grace Roman Space Telescope that's set to launch in 2027. All will conduct redshift surveys of galaxies to assemble vast 3D maps of galactic distribution.

When it comes to the dark universe and how it has affected the growth of galaxies in large-scale structures across the universe, there's still much that we're, well, in the dark about. But with FLI, it's possible to describe the dark-matter distribution associated with the galaxies in the map.

"That’s quite neat, given that we can’t observe dark matter directly, and is complementary to dark-matter maps constructed from gravitational lensing," said Fabian Schmidt.

Ultimately, galaxy mapping isn't just about pictorially describing the universe; it could ultimately plot the path towards revelations about the origins of everything that we see in the cosmos.

The research was published on Nov. 27, 2024 in the journal Physical Review Letters.

Observing the interactions between dark matter and so-called "dark photons" during a period after the Big Bang called the "cosmic dawn" could help shed light on the universe's most mysterious and troubling form of matter.

Dark matter particles outnumber ordinary, everyday matter, which comprises objects like stars, planets, moons, asteroids, cosmic clouds of gas and dust, and all living things, by about five to one. That means all those things listed — and everything else we see in the universe and here on Earth — account for around 15% of stuff in the cosmos, and we have little idea what the other 85% actually is.

Part of the reason this mystery has persisted over the last nine decades or so is that dark matter is effectively invisible because it doesn't interact with particles of light, or "photons," as everyday matter composed of atoms (themselves comprising electrons, protons and neutrons) does.

However, scientists have proposed that photons may have a dark side, too. Dark matter may interact with these so-called "dark photons" just as regular photons interact with matter comprised of atoms.

Now, following this possibility, a team of scientists has proposed that interactions between dark photons and dark matter in the first 500 million years after the Big Bang, aka the cosmic dawn, may have left a "signature" in the universe.

The scientists theorize that this signature could be detected today and used to investigate the mysteries of dark matter.

"Dark photons are theoretical particles that extend the concept of electromagnetism into the 'dark sector.' They are similar to regular photons but interact mainly with dark matter rather than ordinary matter," team member and associate professor at the University of Copenhagen's Cosmic Dawn Center, Charlotte Mason, told Space.com. "Dark photon, dark matter interactions could have produced oscillations — similar to sound waves — that stopped shortly after the Big Bang."

While the fact that dark matter doesn't interact with light or with ordinary matter may seem to suggest it is something of a cosmic ghost, observing the universe but forbidden from interfering, nothing could be further from the truth.

This form of matter played a key role in gathering the first galaxies. That means these hypothetical interactions, known as "dark acoustic oscillations," could hold the secret blueprints of the large-scale evolution of the cosmos under the influence of dark matter.

Come to the darkside... we have photons

Dark matter doesn't interact with light or ordinary matter, but it does interact with gravity, shaping the fabric of space with this influence. This leads to a warping of space, which, in turn, can influence light and ordinary matter. In modern times, this influence has allowed scientists to infer the presence of dark matter, but as Mason pointed out, it had an even more crucial role in the early universe.

That is because, during this time, the first galaxies were thought to have been assembled within a "scaffolding" of dark matter.

"Cosmic dawn is when the first stars and galaxies formed, making it a perfect time to study how dark matter affects galaxy formation," Mason explained. "The way galaxies formed when they formed, and how quickly they formed was highly sensitive to the small-scale distribution of dark matter. This makes Cosmic Dawn an ideal 'laboratory' to test how dark matter behaves and to potentially learn more about its properties.

"Cosmic dawn has been a missing chapter in our understanding of the universe."

Mason added that, thanks to new technologies like the James Webb Space Telescope (JWST) and radio telescopes like the Hydrogen Epoch of Reionization Array (HERA), the Low-Frequency Array (LOFAR), and the Square Kilometer Array (SKA), scientists are finally beginning to explore this period of cosmic history. That is fortunate because cosmic dawn provides a unique insight into dark matter on small scales lost in the modern universe.

"At this early stage, the disruptive effects from galaxies — such as supernova explosions and gas blowing away — were less significant compared to later in the universe’s history," Mason said.

If dark photons existed at cosmic dawn, their interactions with dark matter could have left behind traces of the formation of galaxies.

"The dark acoustic oscillations added small ripples to the density fluctuations created after the Big Bang. This would have influenced galaxy formation by creating regions of higher and lower density, layering on top of the initial fluctuations from the Big Bang," Mason continued. "Galaxies would have formed more quickly in dense areas and more slowly in less dense ones."

That's if we can figure out how to read them. This search must occur at great distances and, thus, further back in time.

"Over time, as gravity caused these fluctuations to evolve, the subtle effects of dark acoustic oscillations are predicted to get smoothed out, so they won't be as easy to detect today," Mason explained.

The team's findings suggest that under specific criteria, despite the subtlety of these signals, one operating radio telescope could be sensitive enough to detect them or, equally importantly, their absence in the near future.

"We discovered that, even after accounting for the complex physics of galaxy formation, if dark matter has oscillations at certain scales, we should be able to detect them (or rule them out) with HERA in the coming years," Mason said. "This is a very exciting prospect!"

"HERA's radio observations are ongoing, so we'll be very excited to see these models tested in their final data analysis," Mason concluded. "Since dark matter is one of the greatest mysteries in physics, any new insights we gain into its nature would be extremely valuable."

The team's research was published at the end of 2024 in the journal Physical Review D.

Somewhere in the multiverse, there could be universes more predisposed to forming stars, and possibly life, than our own universe —- and a new study has shown that it's all thanks to the most unlikely of suspects: dark energy.

A team of scientists has explored how the strength of dark energy directly affects how easily stars form, and it turns out that the strength of dark energy in our universe doesn't lead to the most efficient star factories. In fact, the researchers say that if you select a random observer from anywhere in the multiverse, chances are they'd come from a universe where the strength of dark energy is much greater than it is in our universe.

"That was quite surprising to me!" Daniele Sorini of Durham University, who led the study, told Space.com.

Dark energy is the mysterious force that is accelerating the expansion of the cosmos. The most popular model for dark energy suggests it is the cosmological constant, which describes the intrinsic energy of empty space that is powering the acceleration of the expanding universe. We say that it is "constant" because we think the strength of dark energy has remained the same throughout history.

Suppose, though, that dark energy had a different strength, making the universe's expansion accelerate either faster or slower. Sorini, along with John Peacock of the University of Edinburgh and Lucas Lombriser of the University of Geneva, have modeled how changing dark energy in this way would affect star formation, and because stars are essential for life, how it would affect the habitability of the universe.

To the multiverse!

The crew turned to the multiverse.

The multiverse concept assumes that our universe exists as part of an ensemble of perhaps infinite universes, each with its own distinct characteristics, including possibly different strengths for dark energy.

For life to exist in a universe — life as we know it, at least — that universe needs stars to provide heat and energy to orbiting planets for such life to live on. Sorini, Peacock and Lombriser found in their calculations that the universes most efficient at forming stars have a strength of dark energy —- referred to as the density of dark energy, or how much energy each little piece of space contains — that is one-tenth of the value of dark energy in our universe.

This means that in those more efficient universes, the expansion of space is still accelerating, but only one-tenth as fast. All of the matter in those universes would therefore be much closer together than in our universe.

A universe like this is, the team says, would turn 27% of its gas into stars over cosmic history. Our universe, on the other hand, is expected to convert about 23% of its gas into stars.

But there is a twist in the tale: Suppose you select a random observer from anywhere in the multiverse. An observer (or at least life as we know it) can only exist in a universe that forms stars. If you asked that random observer to describe the strength of dark energy in their corner of the multiverse, chances are that they'll live in a universe where dark energy is stronger than in our universe.

Wait, what?

This sounds like a contradiction. If universes with weak dark energy are the most adept at forming stars — recall that the most efficient universes would have one-tenth the dark energy strength as ours — how can we expect to find most observers in universes with stronger dark energy?

It's all down to statistics, but Sorini has an analogy to help.

"Suppose that you have got many boxes, marked from 1 to 100, and that you are putting marbles into those boxes," he said.

Imagine that you put the most marbles, say 100 of them, into box number 2. Fewer marbles, maybe 10 a-piece, go into the other boxes. In Sorini's analogy, box 2 with the most marbles corresponds to the peak of star-formation efficiency with a dark-energy density one-tenth of our universe's. We might then find our universe as corresponding to box 4 or 5, for example, containing fewer marbles.

However, even though all the boxes numbered 3 to 100 each individually contain fewer marbles than box 2, add them all together and there are more marbles in boxes 3 to 100 combined than there are in just box 2. So, if we were to choose a marble at random, the likelihood is that it will come from a box numbered higher than 2.

"It's a similar thing with the multiverse," said Sorini. In other words, the most efficient star-forming universes have a low value for dark energy, but there are many more universes with much greater values that, while not quite as efficient, still produce stars and result in a habitable universe.

This is only the case up to a point though; dark energy can also theoretically become so strong that it doesn't give any stars a chance to form, or rips apart the universe shortly after some stars do form. Such universes might be represented by boxes 101 and above in Sorini's analogy, each containing no marbles at all.

Lower efficiency, higher quality

Star formation occurs when huge clouds of gas collapse; galaxies form inside massive haloes of this star-forming gas, and the sizes of these haloes are dictated by the interplay between the physics of star formation and the growth of large-scale structures in the universe. Large-scale structures grow more quickly when dark energy is weaker, and more slowly when dark energy is stronger. This is because it's easier for strong dark energy to pull everything apart faster.

However, "the interesting result is that when you've got higher values of dark energy, individual haloes can host galaxies that are more efficient at forming stars," said Sorini.

The reason for this is that, as dark energy increases in strength, the radius of a given halo becomes smaller and more compact because its radius is proportional to both the halo's mass and the Hubble constant, which quantitatively describes the expansion rate of the universe. Because the haloes are more compact, the density of star-forming gas within them is greater — and the denser the gas, the faster the gas cools, so that halo then favors enhanced star formation that requires cold temperatures (below ten degrees above absolute zero) to permit gravitational collapse of the gas into stars. However, because dark energy is working against the formation of large-scale structures, fewer galaxies form in such a universe — therefore, there are fewer stars overall there.

Stars enrich the chemistry of the universe when they expire, releasing the heavy elements formed via nuclear fusion reactions deep inside them. The biochemistry of life on Earth is based on five elements — hydrogen, carbon, nitrogen, oxygen and phosphorus — which build the chemical building blocks that form the nucleotides that assemble into DNA. With the exception of hydrogen, which was produced in the Big Bang, all of these elements are produced by stars. These and other, heavier elements are also the materials used to build planets, which need to orbit stars to receive the light and heat necessary for life as we know it. The more stars form, the more of these elements there are, and the more planets there will be that could support life.

Against the anthropic principle?

The strength of dark energy in our universe has been a source of consternation for scientists ever since the mysterious accelerative force was discovered in 1998. Most theories predict that the cosmological constant in our universe should have a large value, but in reality the strength of dark energy that we observe in our universe is 10^120 times smaller than predicted. That's a big difference — are our best theories really that badly wrong?

We should feel fortunate that dark energy is so weak in our universe. If it were as strong as our theories say it should be, it would have led to a runaway universe that would potentially have torn the fabric of space-time apart in a "Big Rip" long ago, and no life would be able to exist. We'd be in box 101.

But dark energy isn't the only parameter in the universe that seems friendly to support life. The speed of light, the charge of an electron, the mass of a proton, the strength of gravity and the strong force, among others, all seem finely balanced. Were their values even slightly different, the universe would be a changed and more inhospitable place, with stars and life unable to form and develop. What’s more, we don't know why they have the values that we measure. What we do know is that if they didn't have those values, then we wouldn’t be here to measure them.

This paradox is called the anthropic principle, which describes a selection effect in which we measure these values as being so finely tuned for life because we could not exist in a universe where they are not finely tuned — they are a necessity for our existence.

One proposed solution is that our universe is but one universe in a multiverse, which consists of a possibly infinite ensemble of parallel universes which each have fundamental constants with different values. We would be bound to inhabit one of these universes that is friendly to life rather than one that isn't.

It had been assumed that the strength of dark energy was another of the anthropic principle's finely tuned parameters, especially with that puzzling huge discrepancy between theory and observation. But Sorini, Peacock and Lombriser's findings don't seem to quite align with anthropic reasoning because they have shown that other universes could have even more favorable dark-energy strengths.

"I think the key take-home message is to be careful when you apply anthropic reasoning, because the question is actually more subtle than it might look on the surface," said Sorini. "Our findings suggest that you should not use this argument as a get-out-of-jail-free card without more careful reasoning on the assumptions that go behind it."

However, there are some caveats to their findings. For one thing, they assume that dark energy is the cosmological constant, and not a scalar field that can change strength over time. They also assume a certain astrophysical model of star formation; a different model might yield different results. Or perhaps, if the multiverse is real, certain values of dark energy might for some reason be more prevalent than others, meaning that we would need to consider a more complex multiverse in which, in Sorini’s box analogy, a larger number of boxes might have 100 marbles as opposed to 10 marbles.

Isolated islands in an empty sea

While other possible universes might offer more chances for life, it's impossible to say whether they are more inhabited than our own. There are, after all, many more factors involved in the emergence of life than just the efficiency with which a universe forms stars. Suppose though one of these universes with a different dark-energy strength than our universe did have life — what would its inhabitants see? Because dark energy is causing the expansion of the universe to accelerate over time, universes where dark energy is weaker would see its galaxies and galaxy clusters closer together and universes where dark energy is stronger would have experienced much more expansion than our own, transporting galaxies much farther apart from one another.

"The structures that form would be isolated islands in an empty sea," said Sorini. "It could be that we wouldn't even see other galaxies, because everything would be disconnected from us. We would be under the illusion that our galaxy is the only galaxy in the entire universe."

So, while we might be somewhat lucky to exist in our less-optimized universe, having a sky full of galaxies seems much more preferable to being an island in an ocean of nothing.

The research was published on Nov. 13 in the journal Monthly Notices of the Royal Astronomical Society.

A group of astronomers analyzing data from the James Webb Space Telescope (JWST) say some of the oldest galaxies in our universe appear much larger and brighter than expected, suggesting they formed early and grew rapidly — potentially without the influence of dark matter.

According to the researchers, the findings provide new clues that point toward an alternative to dark matter known as modified Newtonian dynamics, or MOND.

"The expectation was that every big galaxy we see in the nearby universe would have started from these itty-bitty pieces," Stacy McGaugh, who is an astrophysicist at the Case Western Reserve University in Ohio, said in a statement. "What the theory of dark matter predicted is not what we see."

The gradual hierarchical evolution of galaxies, which is thought to be driven by cold dark matter and is a crucial component of the standard cosmological model of our universe, is widely accepted because it explains the diverse shapes and sizes of galaxies sprinkled across the cosmos.

Related: Black holes that form in 'reverse Big Bang replays' could account for dark energy

Yet, the JWST has not yet spotted the dim signals expected to emanate from those small, primitive fragments of galaxies in the early universe, McGaugh and his colleagues say. Instead, the telescope's data shows early galaxies were larger and brighter than anticipated, even as the team looked further back in time. The researchers argue that these galaxies grew too big, too quickly — well ahead of expectations set by conventional cold dark matter models.

This rapid growth, however, precisely aligns with the 26-year-old predictions of MOND.

"The bottom line is, 'I told you so,'" McGaugh said in the statement. "I was raised to think that saying that was rude, but that's the whole point of the scientific method: Make predictions and then check which come true."

Some of the excessively bright sources the JWST recorded could be active supermassive black holes instead of galaxies, the researchers note, but that "does not really help anyway, as it simply turns the problem of too many early stars into one of too many early supermassive black holes."

MOND, which posits that, when it becomes extremely weak, gravity behaves differently from the way Isaac Newton predicted it would. An example of such weakness is at the edges of galaxies. The concept was proposed by Israeli physicist Mordehai Milgrom in 1982 as a way to explain faster-than-expected rotation of galaxies without invoking dark matter or dark energy.

Although MOND has had some success, however, it has quite a few critics. Astronomers find it challenging to integrate the idea into a unifying framework that can explain a wide range of cosmological observations. In contrast, the dark matter paradigm fits many observations but doesn't fully explain phenomena predicted by MOND.

"We find ourselves caught between two very different theories that seem irreconcilable despite applying to closely related yet incommensurate lines of evidence," McGaugh and his colleagues wrote in their paper, which was published Tuesday (Nov. 12) in The Astrophysical Journal.

While MOND is not a widely-accepted theory in cosmology, the researchers are convinced it has made enough successful predictions that it cannot be a mere coincidence.

"It must be telling us something," they note in the paper. "What that is remains as mysterious as the composition of dark matter."

It was only a matter of time before artificial intelligence took on dark matter. A new deep-learning algorithm is set to be unleashed upon images of galaxy clusters in search of the telltale signs of this invisible substance that strangely makes up 85% of all matter in the universe.

According to the standard model of cosmology, every galaxy is surrounded by a halo of dark matter. Similarly, galaxy clusters are suffused inside vast haloes of dark matter, which we can detect indirectly. Scientists are also able to determine dark matter's  distribution in a cluster by watching for the way its gravitational influence bends space, therefore creating weak, and sometimes strong, gravitational lenses. Yet, despite the huge volumes of dark matter in the universe, nobody knows what it is made from.

Occasionally, two galaxy clusters — containing galaxies, hot gas and dark matter — can collide. When this happens, how the collision proceeds depends on the nature of dark matter. 

It all comes down to a property of dark matter known as its interaction cross section, which refers to the basis by which dark matter is an unidentified type of particle. One of the reasons astronomers have had so much difficulty tracking down the identity of dark matter is that it doesn't seem to interact with normal matter, other than through gravity. However, some models predict that particles of dark matter can interact with each other, and to what extent this interaction takes place depends upon the interaction cross section.

Related: Dark energy remains a mystery. Maybe AI can help crack the code

So, when two galaxy clusters collide, the fate of their dark matter haloes depends upon this cross section. If the value of the cross section is high, the particles in the two dark matter haloes that are colliding will interact, slowing the dark matter down. Galaxies, on the other hand, will sail on through, rarely actually "colliding" in the way you may think because of the large spaces within stars and other objects within them. Meanwhile, huge clouds of hydrogen in the cluster  do collide, growing hot and radiating X-rays. 

If the value of the interaction cross section is high, the dark matter will separate from the galaxies and get distributed closer to the hot gas clouds.

Alternatively, if dark matter has a small cross section, then the dark matter and galaxies would be separated, but not by as much, with the dark matter found between the galaxies and the hot gas. If the cross section is zero, meaning that dark matter is collisionless, then we should expect the dark matter haloes to stay with the galaxies as they would pass right through each other without interacting at all.

However, there are several complications. One is that we can see only snapshots of galaxy cluster collisions because they take place over time and distance scales that are far too large to reveal progress on human timescales. Furthermore, we are seeing these snapshots all at different stages of collisions and from different angles, so no two galaxy cluster mergers look exactly the same, and it requires a trained eye to pluck what is happening from each example.

A second complication is the effect that winds of radiation from galaxies with active black holes can have. These features are commonly found in the largest galaxies within a cluster, such as M87 in the Virgo galaxy cluster. These radiation winds, described as "feedback" because they directly affect what ultimately instigates them, specifically matter falling towards the central black hole. This feedback can push matter out of a galaxy and into the extragalactic medium within a galaxy cluster, so that ordinary matter ends up where the dark matter might be expected to reside.

To help distinguish among the possibilities, David Harvey of the Ecole Polytechnique Fédérale de Lausanne in Switzerland has written a deep-learning algorithm trained on simulated images of galaxy cluster collisions from the BAHAMAS (Baryons and Haloes of Massive Systems) project conducted by researchers from Liverpool John Moores University, Leiden University, Johns Hopkins University and CNRS in France.

The simulations model galaxy cluster collisions with different cross-sectional values, and even those with no dark matter at all.

Harvey tested different versions of his algorithm, which is a Convolutional Neural Network (CNN) able to recognize patterns in images very well. Harvey found that the most complex version of his algorithm, nicknamed "Inception," was the most accurate, scoring an 80% success rate when challenged to characterize the simulated cluster collisions.

Several projects are already imaging galaxy cluster collisions in an attempt to solve the mystery of dark matter. The Hubble Space Telescope, with assistance from the Chandra X-ray Observatory, has been imaging galaxy cluster collisions for some time now, most famously the Bullet Cluster in 2006. More recently, the European Space Agency launched the Euclid mission, which is designed to study the so-called "dark universe" including the presence of dark matter in clusters. And on a smaller scale, the high-altitude balloon mission called SuperBIT flew around the world for two months in 2023 imaging galaxy cluster collisions, before crash-landing in Argentina. With all this observational data, and more to come, Harvey's "Inception" algorithm will help us find a faster answer to the puzzle that is dark matter.

Harvey's algorithm and its results were described on Sept. 6 in Nature Astronomy.

The Coma Cluster of more than 1,000 galaxies is resplendent in this new image from the powerful Dark Energy Camera (DECam) situated in the four-meter Victor M. Blanco Telescope at the Cerro Tololo Inter-American Observatory in Chile.

Located about 321 million light-years away from us in the constellation of Coma Berenices, the Coma galaxy cluster has made a significant mark in our study of dark matter. In 1937, it was within this cluster where Caltech astronomer Fritz Zwicky first found evidence for the existence of dark matter. He noticed that the galaxies in the cluster were moving faster than the gravitational field generated by all the cluster's visible matter should allow. In fact, the galaxies were moving so fast that, by all rights, they should have flown right out of the cluster and escaped into deep space. Zwicky thus deduced that there must be a substantial amount of invisible, or "dark," matter present in the Coma Cluster, but his ideas at the time were considered too radical. 

It was only in the late 1960s and early 1970s, when Vera Rubin and Kent Ford systematically found evidence for dark matter in galaxies by studying their rotation curves — that is, how fast the stars and gas in those galaxies are moving — that astronomers became serious about dark matter. 

Today, we know that 90% of the mass of the Coma Cluster is made from mysterious dark matter.

Since those early dark matter milestones, a combination of observations and theory have also resulted in the standard model of cosmology, which depicts a universe threaded by a cosmic web of dark matter and laced with normal matter in the form of gas and dust. Galaxies tend to form along the filaments of this web, and at the nodes of the web where the filaments interlink, we find galaxy clusters.

Related: Dark Energy Camera captures record-breaking image of a dead star's scattered remains

A 2020 study from a team led by Nicola Malavasi of the Ludwig–Maximilians–Universität in Germany found that the Coma Cluster is linked to three separate cosmic-web filaments, with two of the filaments particularly prominent. Dark matter, gas and even whole galaxies flow along the filaments and fall into the Coma Cluster where the filaments meet. One of the filaments is found on the west side (from our point of view when seen on the sky) of the cluster and coincides with an X-ray emitting shockwave generated by infalling matter from the filament colliding with the intra-cluster medium — that is, the hot gas that fills the space between the galaxies in the cluster. 

Another filament is found connecting the north-east corner of the Coma Cluster and is associated with the small group of galaxies that surrounds the giant elliptical galaxy NGC 4839, which is currently falling into the cluster. In particular, this filament is bringing in pristine, cold hydrogen gas that is sparking fresh star formation in that corner of the cluster. It also shows that the Coma Cluster is still accreting matter and growing in mass via these filaments. In general, the more filaments there are connecting to a cluster, the more massive that cluster is and the faster galaxy evolution seems to proceed, with a greater abundance of red elliptical and lenticular galaxies where star formation has virtually ceased.

Earlier this year, astronomers based in South Korea and the United States were able to apply what's known as a weak gravitational lensing technique to find intracluster filaments of dark matter extending through the Coma Cluster. These intracluster filaments are like tendrils at the end of the larger cosmic-web filaments, and in fact feed dark matter into the cluster. They were found using the Hyper Suprime-Cam on the Subaru Telescope on Mauna Kea, Hawaii, which detected the subtle effect of the mass of the dark matter filaments creating enough gravity to warp space just enough to slightly distort the light of galaxies around them. Hence, we call this "weak" lensing, as opposed to strong lensing that magnifies light from much farther objects.

Cosmic web filaments can link neighboring galaxy clusters too, with a filament connecting the Coma Cluster to the Leo Cluster, and together the pair form the Coma Supercluster of more than 3,000 galaxies, spanning 20 million light-years across space.

Despite its name, the Dark Energy Camera that produced this shot of the Coma Cluster has since retired from duties scrutinizing dark energy, following its stint leading the Dark Energy Survey between 2013 and 2019. Now, the 570-megapixel astronomical camera has become a general workhorse, routinely producing incredible images — including this one.

If you've been perusing our website, you've probably noticed by now that this July marks 25 years for Space.com. Fittingly, we've been celebrating this period by noting the incredible discoveries and breakthroughs in space science that have happened in the last quarter century. However, there is a dark cloud on the horizon of this celebration.

Two gatecrashers have turned up to the party to remind us that the last two and a half decades haven't only been filled with science victories. Nope, two constant and perpetual mysteries have stubbornly refused to be solved. In fact, many of the advancements made over the last 25 years regarding these elements of the universe have only served to deepen the shroud of confusion that obscures their true nature.

We are, of course, referring to dark energy and dark matter, sometimes collectively referred to as the "dark universe." But the relationship between the dark universe and Space.com actually runs deeper than our coverage of the substance's investigation. Dark energy was discovered in 1998, just a year before we were founded. We'll start there.

"1999 was indeed quite important for the astronomical community as well as Space.com because it is the first full year in which we knew that the universe is not only expanding, but it is doing it at an accelerated rate," Universidad ECCI cosmologist Luz Ángela García Peñaloza told Space.com. "That is why 1999 marked a paradigm shift in the cosmological standard model. We started postulating the existence of an additional component in the cosmos's matter-energy content: dark energy."

Related: 25 years of exoplanet hunting hasn't revealed Earth 2.0 — but is that what we're looking for?

Thus, you could say that Space.com and dark energy have grown up together — and during this growth, we also charted the progress of its older dark universe sibling, dark matter, the birth of which (theoretically, at least) dates back to 1933.

"The notion of dark matter has evolved to the idea of a dark sector, with both dark matter and dark energy playing concrete and observationally established cosmological roles," Susan Gardner, a theoretical particle physicist at the University of Kentucky, told Space.com.

To understand why the dark universe is so problematic for researchers, it is apt to discuss what we do know about these aspects of the universe. One of the most important factors to consider is the utter dominance of the dark universe.

Dark matter and dark energy are big problems

We live in an epoch of the universe that is distinguished by the rule of dark energy, the force that, as Garcia Peñaloza explains, drives the accelerating expansion of the universe. Dark energy is estimated to account for between 68% and 72% of the universe’s total energy and matter contents, or "budget," thus heavily dominating both dark matter and ordinary matter.

Dark matter has less of a stranglehold on the cosmos, accounting for around 26% of the universe's total energy and matter budget. Yet, this is enough to ensure that dark matter outweighs the matter that comprises every star, every planet, every moon, every cloud of dust and gas, every human, cell phone, printer, post-it note, and cat in the cosmos — at a staggering 5 to 1 ratio.

Of course, the dominance of the dark universe just illustrates the scale of this problem; it isn’t the crux of it. The real problem is that, despite their ubiquity, dark matter and dark energy remain elusive. They seem to be extensions to the Standard Model of particle physics, which is the most detailed model we have of how all the particles in our universe interact with one another. Any extension to this model threatens its stability, and therefore our knowledge of the entire universe's physics.

Take dark matter, for instance. 

The concept was first theorized by Swiss American astronomer Fritz Zwicky in 1933, when he found that the mass of all the stars in the Coma cluster of galaxies only provided 1% of the gravitational influence needed to keep these galaxies from escaping the cluster's gravitational pull. This was solidified in 1978, when astronomer Vera Rubin studied the rotation of galaxies, finding their rotational speed means the gravitational influence of visible matter in the galaxies would not be sufficient to hold them together. In other words, dark matter was posited as the glue sticking galaxies together, exerting an unseen gravitational influence to bolster what the ordinary contents of galaxies can offer. 

While this influence allows dark matter's presence to be inferred through its effect on normal matter and on light, however, dark matter is effectively invisible to us. That's because it doesn’t interact with light or ordinary matter directly. It is this lack of interaction (or the existence of an extremely weak interaction that isn’t detectable by our current technology) that tells scientists dark matter can't be made up of atoms composed of protons, neutrons and electrons — all part of the "baryon" family of standard matter because these particles do interact with light, and with each other. This has prompted the search for particles beyond the Standard Model that could compose dark matter; the hunt that has consumed scientists for the past 25 years.

"I would say the leading dark matter candidates in 1999 were dark matter weakly interacting massive particles, or 'WIMPs' and axions, which were first introduced as a possible explanation for the strong CP problem [the fact that the laws of the universe seem to treat matter and antimatter differently]," Gardner said. "Both candidates are very much with us, but how they emerge from theoretical models has definitely changed with time."

She added that some dark matter particle candidates seem to have died in the last 25 years, but even these are occasionally revisited, meaning a resurrection can't be fully ruled out. 

Gardner said an example of this is ultraheavy particles called charged massive particles, or  "CHAMPs." These seemed to have fallen out of favor around 30 years ago in the 1990s, before dark energy was even discovered and Space.com was founded. However, CHAMPs were revisited by a team of authors as recently as 2020, so it is hard to fully dismiss their comeback as dark matter suspects.

"It seems hard to kill off particular dark matter candidates altogether," Gardner added.

One thing scientists would definitely love to kill, though, is the term "dark energy." While the "dark" prefix in both "dark matter" and "dark energy" refers to their mysterious and "invisible" nature, the former is more categorically a placeholder name for whatever this accelerating force is. While dark matter was expected by some scientists since the 1930s, around when Zwicky coined the concept, whatever dark energy is, it came as a complete surprise.

Out of nowhere!

At the beginning of the 20th century, Edwin Hubble managed to observe distant galaxies undergoing what's known as "redshift." As light travels across the universe on the way to reaching our detectors on Earth, its wavelengths sort of stretch out like rubber bands during the journey. They go from shorter, blueish wavelengths to longer, reddish ones; the longer light travels, the redder it appears. This means that if an astronomer detects light rays coming from a galaxy progressively headed toward the red end of the electromagnetic spectrum, that galaxy is probably moving away from us. So, when Hubble made this discovery, it indicated that the universe isn't static. It's actually expanding.

This took scientists of the time by surprise, as the consensus had been that the universe was static. This idea was so prevalent that when Albert Einstein devised an equation of the universe based on his theory of gravity, general relativity, he introduced a "fudge factor" called the "cosmological constant" represented by the Greek letter lambda that would counter the attractive force of gravity and keep the universe static.

Once Einstein was thoroughly convinced that Hubble was correct about the expanding universe, however, he scrapped the cosmological constant, later describing its addition as his "greatest blunder." Yet, before the 20th century was done, the expanding universe would deliver a further shock to scientists, and one that would require the cosmological constant to be rescued from the theoretical trash can.

In 1998, two separate teams of astronomers making observations of distant cosmic explosions called Type Ia supernovas — which are called "standard candles" because their uniform light output can serve as buoys in the ocean of space and help scientists measure cosmic distances — found that galaxies further from us are moving away faster. 

García Peñaloza explained that this discovery showed that the universe isn’t just expanding; this expansion is accelerating. Dark energy was introduced as a placeholder for whatever force is driving that acceleration. 

The dark energy-driven epoch of the universe is separate and distinct from the initial period of rapid cosmic inflation that is now commonly called the "Big Bang," which saw the volume of our universe increase by a factor of 10^26 (10 followed by 25 zeroes). This rapid Big Bang-driven inflation slowed to a near halt as matter came to dominate the universe, however.

But when the universe was just under 10 billion years old, something very strange happened. The cosmos suddenly began to expand rapidly yet again, with that expansion getting faster and faster, and this acceleration continuing today. This third significant period of the universe is called the dark-energy-dominated epoch. That's what we're presently in.

To consider how strange this was to scientists, compare it to an Earth-bound analogy: pushing a child on a swing. You give the swing one big push, and you watch it reach a high point, then swing back and forth while reaching a lower and lower point with each oscillation and simultaneously slowing down. Then, just as the swing has almost stopped, suddenly and for no discernable reason, imagine it begins oscillating again. Plus, rather than reaching an initial high point and then coming to lower points with each oscillation, the swing gets higher and higher over time, and moves faster and faster. That is akin to what the universe is doing in this dark-energy-dominated epoch we are currently in.

Just as you would really want to know what gave that swing the second push and how it is getting stronger, scientists desperately want to know what gave the universe a "second push" around 4 billion years ago. And just as the force driving the swing will determine the fate of the child — will they eventually fly into the bushes or into the stratosphere? — the nature of dark energy will determine the fate of the universe. Will the cosmos die as a frozen remnant with galaxies too widely separated to be seen from each other, will the very fabric of space and time "tear," or will the universe "snap back" on itself and contract?

"Although there have been multiple efforts to understand the nature of dark energy, its composition, and its manifestation in the universe — both from theoretical and observational perspectives — we know embarrassingly little about it," García Peñaloza said. "By far, the leading candidate for dark energy is the reintroduced cosmological constant [still represented with the Greek letter lambda], and it has been related to the vacuum energy of quantum fluctuations." This means virtual particles literally pop into existence in the vacuum of space. It sounds impossible, but it is indeed possible if two particles appear with equal and opposite energies and then rapidly annihilate each other. It is almost as if the universe has an overdraft facility for energy.

This accounts for dark energy in what has become the "standard model of cosmology," also known as the lambda cold dark matter model (LCDM), in which "cold" refers to dark matter particles moving slower than the speed of light. García Peñaloza explained that one alternative to the LCDM model is the wCDM model in which dark energy has a constant value, a cosmological equation of state parameter called "w," which represents the balance of the universe's pressure to its energy density.

"Dynamical dark energy models have also been shown to be compelling competitors to lambda, such as quintessence, a scalar field that evolves in time, a linear evolution of the equation of state called Chevalier-Polanski-Linder (CPL), and a very extensive list of theories that have been proposed and tested against the observables, with different physical motivations," García Peñaloza continued. "My colleagues and I have our own model of dark energy, one that evolves in the early universe as radiation and then transitions to the cosmological constant's equation of state at late times. But, I guess what matters, in this case, is what shows the observational evidence, which is increasing with new telescopes online and facilities around the world and more sophisticated simulations that now can include your favorite 'flavor' of dark energy."

The future is bright for the dark universe

The fact that dark energy remains a frustratingly unknown quantity in the universe doesn’t mean that absolutely no progress has been made while deciphering it over the last 25 years, however. In particular, García Peñaloza thinks a development that took place this year will be particularly important for the further unraveling of this mystery.

"In my opinion, the recent year one results released by the Dark Energy Spectroscopic Instrument (DESI) collaboration have been particularly interesting because it is the first time that blinded observations disfavored the cosmological constant, but instead showed that dark energy could be varying with time," she said. "A big disclaimer here is that these are just the first year of observations of the collaboration, so the results could change in the future with a more extensive catalog of galaxies surveyed." García Peñaloza added that the James Webb Space Telescope (JWST) has also introduced tension in our current understanding of the properties of early galaxies and theoretical models that include the cosmological constant as their backbone.

"All these observations are providing us with hints that probably the Standard Model needs some adjustments," she added. "I just feel it is a very exciting moment to be working in this topic."

Additionally, NASA's Nancy Grace Roman Space Telescope and the Earth-based Vera C. Rubin Observatory will soon start exploring the universe, with both telescopes expected to deliver major dark matter and dark energy findings.

So, does Gardner think that, at some point in the next 25 years, Space.com will be reporting on a solution to the puzzle of dark matter?

"I'd like to bet 'Yes!'" she responded. "We may yet be able to detect heavy dark matter in terrestrial laboratories via its gravitational couplings, and we may be able to use gravitational wave detectors to discover or to set limits on heavy solar-system dark matter."

When asked the same question about dark energy, he was less confident.

"Tough question! I'm gonna say 'No,' she said. “For sure, we will know much more of the nature of dark energy than we know now, or maybe we will rule it out completely from the landscape. Let's stay tuned with the developments that astronomers do in these coming years, and maybe we will have the answer to this question."

You can guarantee whatever develops in the next 25 years with regards to dark matter and dark energy, Space.com will definitely be staying tuned to the dark universe, and we hope you will stay tuned to us!

The Hubble Space Telescope has shown that dark matter is concentrated within the core of a nearby dwarf galaxy, a finding that rushes to the rescue of the Standard Model of cosmology. This model basically predicts dark matter to be "cold," but recent findings have started to hint at the substance being "warm." These new observations, however, are on the Standard Model's side.

Dark matter is the invisible substance purported to make up 85% of the mass of the universe, but nobody knows what dark matter actually is, or exactly how it behaves. Our best idea is that it is "cold," which, in other words, means it is predicted to consist of a low-energy particle that's not zipping about hither and thither, but is rather slow-moving and capable of clumping together to form huge haloes inside which galaxies grow. The concept of cold dark matter (CDM) and its influence on structure formation in the universe is a critical part of our current Standard Model of cosmology. That part is known as Lambda–CDM (the lambda refers to dark energy).

In the cold dark matter paradigm, dark matter should especially pile up in the core of a dark matter halo, hence dark matter should be densest in the core of a galaxy that grows inside that halo. Astronomers call this the dark matter "cusp" because of the shape it makes on a graph of dark-matter density relative to its radius from the center of a galaxy.

However, astronomers have been stumped by some recent observations of dwarf galaxies that have hinted that dark matter might behave differently than they thought. Instead of acting like cold dark matter and clumping most densely in the core of the dark matter halo, these observations imply that dark matter may be more evenly distributed throughout a galaxy instead. This would be a sign that dark matter is "warm," or have  enough energy to not clump together so much. If true, this would have significant repercussions for our cosmological models that rely on dark matter being able to clump in certain ways.

Related: Hubble Space Telescope finds closest massive black hole to Earth — a cosmic clue frozen in time

Now, astronomers led by Eduardo Vitral of the Space Telescope Science Institute (STScI) in Baltimore, Maryland, have put this to the test. 

Dwarf galaxies are the best place to study dark matter because, proportionally, they have the highest abundance of dark matter of any galaxy type. The Draco dwarf galaxy, which was chosen for this study, orbits our Milky Way galaxy at a distance of 250,000 light years from Earth. In Hubble's archives, there is data describing the motions of stars in the Draco dwarf spanning 18 years, between 2004 and 2022. Vitral's team were able to use these motions to calculate an accurate measurement of the Draco dwarf’s gravitational field, and hence the distribution of its mass, including the part dedicated to dark matter.

By combining the "proper motions" of the stars — that is, their motion across the sky — with their radial motions toward or away from us that is detectable as either a blueshift or a redshift in light, Vitral's team was able to track the movements of the stars in the Draco dwarf in 3D. 

"When measuring proper motions, you note the position of a star at one epoch and then many years later measure the position of that same star. You measure the displacement to determine how much it moved," said team-member Sangmo Tony Sohn of STScI in a statement. "For this kind of observation, the longer you wait, the better you can measure the stars shifting."

Certainly, Hubble's longevity in space is an advantage here, as is its powerful resolution from its vantage point high above Earth's turbulent atmosphere. The proper motion of the Draco dwarf's stars over the course of 18 years at a distance of a quarter of a million light years is tiny, equivalent to less than the width of a golf ball on the moon as seen from Earth. Hubble's results are therefore the most detailed measurements of stellar motions in another galaxy ever made.

Using these stellar motions, Vitral's team was able to conclude that the total mass of the Draco dwarf's dark-matter halo, out to a radius of nearly 3,000 light years, is 120 million times the mass of our sun. Furthermore, the results strongly indicate that the Draco dwarf's dark-matter density profile does have a cusp in the core and that therefore dark matter is probably cold. As the researchers write in their research paper, "The results lessen the tension around the ‘cusp-core’ problem and give further credence to standard lambda-CDM cosmology."

"Our models tend to agree more with a cusp-like structure, which aligns with cosmological models," said Vitral in the statement. "While we cannot definitively say all galaxies contain a cusp-like dark-matter distribution, it’s exciting to have such well measured data that surpasses anything we've had before."

The next step, therefore, is to repeat the analysis for other dwarf galaxies, and Vitral's team are currently working on studies of the Sculptor and Ursa Minor dwarf galaxies, which also orbit our Milky Way galaxy.

If the findings can be repeated in those and other galaxies, it would effectively rule out some dark matter candidates such as sterile neutrinos and gravitinos, the latter being a hypothetical particle predicted by the theory of supersymmetry as being the massive partner to the equally hypothetical (but probably real) graviton. The results therefore strengthen the possible models of cold dark matter, principally weakly interacting massive particles (WIMPs), primordial black holes and axions.

The results from the Draco dwarf were published on July 11 in The Astrophysical Journal. 

Scientists have used supercomputers to create a "synthetic universe" that will help predict what the next generation of super-telescopes will see upon opening their eyes to the cosmos.

These telescopes will both be "dark universe" detectives in that they will investigate the two most pressing mysteries in cosmology: dark energy and dark matter, sometimes referred to collectively as the "dark universe." Notably, the news comes as the $10 billion James Webb Space Telescope (JWST) celebrates two years of delivering scientific results today, July 12. The JWST has had an immense impact on astronomy, with researchers still working to understand some of the surprising things it has seen.

The newly generated synthetic cosmos should help scientists avoid at least some of the same elements of surprise when both NASA's Nancy Grace Roman Space Telescope and the Vera C. Rubin Observatory start exploring the universe, though these telescopes will undoubtedly still reveal some unexpected delights of their own.

This simulated universe was created with the Theta supercomputer at the Argonne National Laboratory in Illinois as part of a wider project called OpenUniverse. 

Related: Weird physics at the edges of black holes may help resolve lingering 'Hubble trouble'

The copycat cosmos consists of nearly 4 million simulated images depicting the universe as it should appear to Roman, set to launch in 2027, and the Earth-based Rubin, currently under construction at the peak of Cerro Pachón, a mountain in northern Chile.

"Using Argonne's now-retired Theta machine, we accomplished in about nine days what would have taken around 300 years on your laptop," Katrin Heitmann, deputy director of Argonne's High Energy Physics division, who managed the project's supercomputer time, said in a statement. "The results will shape Roman and Rubin's future attempts to illuminate dark matter and dark energy while offering other scientists a preview of the types of things they’ll be able to explore using data from the telescopes."

Illuminating the dark universe

Despite being very different observatories, Roman, located around a million miles from Earth, and Rubin, located at high altitudes in the dry and clear atmosphere of northern Chile, will both investigate the mystery of dark energy. 

"Dark energy" is a placeholder name for the mysterious force driving the ever-accelerating expansion of the cosmos; the nature of such expansion remains a mystery itself. This substance has proven troubling for scientists because dark energy dominates the universe, accounting for around 68% to 70% of the total matter-energy budget of the cosmos.

The OpenUniverse simulation could help scientists better understand the signatures of dark energy they will see when Roman and Rubin start delivering images. This could mean that even faint fingerprints of dark energy could yield important scientific results right out of the gate.

"OpenUniverse lets us calibrate our expectations of what we can discover with these telescopes," Jim Chiang, a scientist at the National Accelerator Laboratory who helped create the simulations, said in the statement."It gives us a chance to exercise our processing pipelines, better understand our analysis codes, and accurately interpret the results so we can prepare to use the real data right away once it starts coming in."

Roman and Rubin will also be influential in understanding dark matter, which accounts for around 26% of the remaining matter and energy in the cosmos. This mission will be particularly poetic for Rubin because it is named for Vera Rubin, the American astronomer who established the presence of dark matter in galaxies.

Dark matter is problematic because it does not interact with light nor ordinary matter  — or, if it does, these interactions are so weak and rare we can't detect them. This means dark matter can't be composed of electrons, protons and neutrons like everyday matter is. That's because everyday matter certainly interacts with light, and with itself.

Astronomers can only infer the presence of dark matter from its interaction with gravity, which, in turn, influences everyday matter and the passage of light.

Rubin and Roman — named after Nancy Grace Roman, NASA's first head of science, affectionately known as the "mother of Hubble" and who pushed for powerful space telescopes to be built in the first place — will hunt for these effects.

This dark universe investigation set to be undertaken by Rubin and Roman will be no mean feat. Rubin, set to begin operating in 2025, will rely on the largest digital camera ever built to investigate the dark universe, while Roman will offer a much wider view of the cosmos than the Hubble Space Telescope or the JWST can.

In fact, even simulating what these telescopes would see was a complicated task requiring a huge amount of computing power. Now that its is done, however, the OpenUniverse team is confident the benefits will soon be self-evident.

"We made phenomenal strides in simplifying these pipelines and making them usable," Kiessling concluded. "Now we want people to start working with the simulations to see what improvements we can make and prepare to use the future data as effectively as possible."

On Thursday (May 23) the European Space Agency (ESA) and its collaborators released a set of five images constructed by its revolutionary space telescope Euclid. The Euclid consortium had previously released five images from the space telescope on November 7, 2023.

Euclid has been labeled Europe's "dark universe detective" because its wide field of view allows it to track billions of galaxies across 10 billion years of cosmic history, enabling astronomers with tools that can reveal more about two mysterious elements of our cosmos: dark energy and dark matter. 

Even before getting to work on collecting scientific data to unravel the mysteries of dark energy and dark matter, however, collectively referred to as the "dark universe," Euclid demonstrated its potential with these two incredible sets of images. 

As such, Space.com asked several scientists in different fields to explain which of Euclid's images from the two releases are their favorites thus far, and why.

Related: The Euclid 'dark universe detective' telescope has revealed new images of the cosmos — and they are remarkable

But first, dark universe 101

Dark energy is the placeholder name given to the force accelerating the expansion of the universe, pushing galaxies away from each other faster and faster. Looking at galaxies that existed when the 13.8 billion-year-old universe was just around 4 billion years old could thus reveal how this force has evolved over time, helping determine its true nature.

Dark matter, on the other hand, is a form in the universe that's virtually invisible because it doesn't interact with light. This means it can't be comprised of the particles that make up the "ordinary" matter. Because it does have a gravitational influence, however, haloes of dark matter have affected the development of the largest structures in the universe. The field of view of Euclid is wide enough to capture these structures in one image, meaning it could help crack the case of how dark matter has influenced galactic evolution.

Dark energy accounts for around 67% of the universe's energy and matter budget, while dark matter accounts for around 27%. That means the "dark universe" collectively accounts for around 95% of the universe's contents, with stars, planets, the moon, humans, cats and the rest of everyday "stuff" that we understand (maybe not cats, to be fair) accounting for only 5% of the universe. That makes the "dark universe" a big problem, to put it lightly.

Euclid takes a walk on the dark side

Luz Ángela García Peñaloza is a cosmologist at the Universidad ECCI in Columbia who studies the mystery of dark energy and its influence on cosmic evolution. That means she's been watching the development of Euclid with great interest.

"Euclid is observing the universe in a brand new way, and it's going to generate a gigantic census of the galaxies. Personally, I find it fascinating how beautiful these first photos look, as well as all the amazing information that they will reveal," García Peñaloza told Space.com. "I had to take a deep breath when I saw the images because of their beauty and because of their high resolution."

When asked to pick her favorite image from the Euclid releases, García Peñaloza selected one of the galaxy cluster Abell 2390 (below).

"It is just breathtaking," she said. "Any image that reveals information about the distribution of galaxies in the large-scale structure of the universe will provide handfuls of information about the nature of the 'dark side' of the cosmos."

Italian astrophysicist Andrea Botteon from the Istituto di Radioastronomia: IRA (INAF-IRA) also selected the Abell 2390 image as his favorite of Euclid's new set.

"As an astrophysicist working on galaxy clusters, I can tell you that my favorite of the new release is the image of Abell 2390," Botteon said. "Together with the earlier released image of the Perseus Cluster [below], it shows the capability of Euclid to recover the very low surface brightness emission from galaxies and especially the intra-cluster light!"

Amateur astronomer Giuseppe Donatiello has discovered 11 galaxies in astronomical survey data, nine of which are named after him, cementing his place in astronomy textbooks. He explained that every expert will pick a different image from Euclid as their favorite based on their area of study. He definitely has a top pick himself, and it comes from the Nov. 2023 batch of images from Euclid. 

"As a fan of Local Group and dwarf galaxies in the Local Universe, I was impressed by the detail in NGC 6822," Donatiello told Space.com. "I have viewed images of that galaxy taken with all the most powerful ground-based instruments, but the detail and depth of Euclid are at a much higher level. Clusters, nebulas, and [globular clusters] are easily recognizable in the Euclid image instead of blurry details. I got lost in that field of view for hours!"

Donatiello also selected his favorite image from the latest Euclid releases.

"Of the new ones, the most interesting for me is NGC 6744 due to the fine details in the galaxy's spiral arms," Donatiello continued. "I also do work that deals with stellar streams [stars and gas pulled from their galaxies by tidal forces], and the Euclid images contain information about stellar streams that I just cannot get in lower-resolution images. I hope the first public data release [DR1] from Euclid is as usable as data from other deep surveys are. 

"If that is the case, I'll have fun!"

David Kipping is an assistant professor of astronomy at Columbia University who investigates the existence of moons around planets outside the solar system. He has also chosen an image from the previous release as his favorite Euclid picture thus far.

"These are gorgeous images that really show off the impressive field of view. The Horsehead Nebula has to be my favorite!" Kipping told Space.com. "Of course, these images are mostly for public consumption rather than science, so I'm especially looking forward to seeing the early science results."

This new set of images and the previous set are part of Euclid's Early Release Observations and were collected before 14 February 2023, when the space telescope began its main science operations. Thus, both sets of spectacular images represent only a tiny fraction of the observations the telescope will make over the next six years during its primary mission.

García Peñaloza said that while these new images and the previous set show that Euclid is living up to expectations, the space telescope still has much to offer.

"This is just the beginning of what we will be able to see in Euclid’s lifetime," García Peñaloza concluded. "I'm positive Euclid will shed light on our understanding of many cosmic mysteries. The best is still to come from Euclid!"