The most accurate observation to date of distant stars that periodically change in brightness may spark a rethink of the rate at which the universe expands — perhaps by settling a longstanding problem in cosmology, or deepening it.
The observation confirms a disparity that exists between the two major methods of measuring how fast the universe is expanding, conforming with one but not the other, a new study reports.
Researchers with the Stellar Standard Candles and Distances group used data collected by Europe's Gaia spacecraft to study Cepheid variable stars, which pulsate in a regular manner, providing a way of accurately measuring cosmic distances. The Cepheid star measurement technique expands on other methods, such as one that relies on observations of Type 1a supernovas.
Related: Hubble telescope refines universe expansion rate mystery
The light output of supernovas, mammoth explosions that occur at the end of big stars' lives, is so uniform they are referred to as "standard candles" and form an important part of what astronomers call the "cosmic distance ladder." The Cepheid star distance measurement method adds another "rung" to that metaphorical ladder, and this new research has strengthened that rung.
"We developed a method that searched for Cepheids belonging to star clusters made up of several hundreds of stars by testing whether stars are moving together through the Milky Way," study co-author Richard Anderson, a physicist at the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland, said in a statement.
"Thanks to this trick, we could take advantage of the best knowledge of Gaia's parallax measurements while benefiting from the gain in precision provided by the many cluster member stars," Anderson said. "This has allowed us to push the accuracy of Gaia parallaxes to their limit and provides the firmest basis on which the distance ladder can be rested."
The cosmic distance ladder is also used to measure the expansion rate of the universe, known as the Hubble constant. This new recalibration of the Cepheid "rung" deepens a problem with the rate at which the universe expands, which has come to be known as the "Hubble tension."
What is the Hubble tension?
In the early 20th century, shockwaves rippled through physics and astronomy when Edwin Hubble uncovered evidence that the universe is not static, as was believed at the time, but is actually expanding. This rate of expansion therefore became known as the Hubble constant.
This concept underwent a major shakeup in the late 1990s, when astronomers discovered via the observation of distant supernovas that, not only is the universe expanding, but it is doing so at an accelerating rate. Since then, measuring the Hubble constant has become a thorny issue for astronomers and cosmologists, because there are two major ways of determining this value — and they don't agree.
One method uses galaxies' velocities as a function of distance to deliver a Hubble constant value of about 73 ± 1 kilometers per second per megaparsec (km/s/Mpc), with 1 Megaparsec representing around 3.26 million light-years. This is known as the "late time" solution, because it comes from measurements of the universe in recent times.
The other method of measuring the Hubble constant looks at the light from an event shortly after the Big Bang called "the last scattering," in which electrons combined with protons to form the first atoms. As free electrons had previously scattered photons (particles of light) dramatically, preventing them from traveling very far, this event meant that light was suddenly allowed to travel through the cosmos freely.
This "first light" is now seen as the cosmic microwave background (CMB), and it almost uniformly fills the cosmos, barring tiny variations. When astronomers measure these tiny variations in this fossil radiation, it predicts a modern-day value for the Hubble constant of around 67.5 ± 0.5 km/s/Mpc.
The differences between the two estimations of the Hubble constant have strangely only grown as measuring techniques for both have been refined and have become more precise. This 5.6 km/s/Mpc difference, and the general trouble surrounding it, is referred to as the "Hubble tension." It's a serious issue for cosmologists, as it suggests there is something wrong with our understanding of the basic physical laws that govern the universe.
Related: The universe is expanding so fast we might need new physics to explain it
Cepheid variables pick a side
Anderson explained why a difference of just a few km/s/Mpc in the Hubble constant matters, even given the vast scale of the universe. (The width of the observable cosmos alone is estimated to be around 29,000 MPC.)
"This discrepancy has a huge significance," Anderson said. "Suppose you wanted to build a tunnel by digging into two opposite sides of a mountain. If you've understood the type of rock correctly and if your calculations are correct, then the two holes you're digging will meet in the center. But if they don't, that means you've made a mistake — either your calculations are wrong or you're wrong about the type of rock."
Anderson said that is analogous to the Hubble tension and what's going on with the Hubble constant.
"The more confirmation we get that our calculations are accurate, the more we can conclude that the discrepancy means our understanding of the universe is mistaken, that the universe isn't quite as we thought," he added.
The improved calibration of the Cepheid variable measurement tool means that this technique finally "takes a side" in the Hubble tension debate, providing agreement with the "late time" solution.
"Our study confirms the 73 km/s/Mpc expansion rate, but more importantly, it also provides the most precise, reliable calibrations of Cepheids as tools to measure distances to date," Anderson said. "It means we have to rethink the basic concepts that form the foundation of our overall understanding of physics."
The team's results have other implications as well. For example, the more accurate Cepheid calibration also helps to better reveal the shape of our galaxy, study team members said.
"Because our measurements are so precise, they give us insight into the geometry of the Milky Way," study lead author Mauricio Cruz Reyes, a Ph.D. student in Anderson's research group, said in the same statement. "The highly accurate calibration we developed will let us better determine the Milky Way's size and shape as a flat-disk galaxy and its distance from other galaxies, for example."
The new study was published last week in the journal Astronomy & Astrophysics.
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"Space DOES NOT Expand Everywhere...Is the space inside, say, a galaxy growing but overcome by the gravitational attraction between the stars? The answer is no. Space within any gravitationally bound system is unaffected by the surrounding expansion." bUHZ2k9DYHY:356View: https://youtu.be/bUHZ2k9DYHY?t=356
Sabine Hossenfelder: "The solution of general relativity that describes the expanding universe is a solution on average; it is good only on very large distances. But the solutions that describe galaxies are different - and just don't expand. It's not that galaxies expand unnoticeably, they just don't. The full solution, then, is both stitched together: Expanding space between non-expanding galaxies...It is only somewhere beyond the scales of galaxy clusters that expansion takes over." https://www.forbes.com/sites/startswithabang/2017/07/28/most-things-dont-actually-expand-in-an-expanding-universe/
Expanding space with non-expanding patches, per se, is nonsense of course, but it becomes utmost idiocy if we combine it with another nonsense - light stretched by expansion:
"The universe is expanding, and that expansion stretches light traveling through space in a phenomenon known as cosmological redshift." https://www.nasa.gov/feature/goddard/2019/nasa-s-webb-to-explore-galaxies-from-cosmic-dawn-to-present-day
"As light travels towards us from the distant galaxies, it is stretched over time by the ever expanding space it is travelling through. The longer it travels, the more the wavelengths are increased (reddened)." https://www.wwu.edu/astro101/a101_hubble_redshift.shtml
How can stretching of light occur if part of space is expanding and the other part is not expanding? The scenario is more than preposterous: Light is stretched as it travels in the space between galactic clusters, then stretching stops as the light enters a cluster, then stretching continues as the light leaves the cluster, etc. Idiotic, isn't it? Unfortunately, in Einstein's world, just like in Big Brother's world, even the most obvious idiocy can be universally accepted and even worshiped:
George Orwell: "In the end the Party would announce that two and two made five, and you would have to believe it. It was inevitable that they should make that claim sooner or later: the logic of their position demanded it. Not merely the validity of experience, but the very existence of external reality, was tacitly denied by their philosophy. The heresy of heresies was common sense. And what was terrifying was not that they would kill you for thinking otherwise, but that they might be right. For, after all, how do we know that two and two make four? Or that the force of gravity works? Or that the past is unchangeable? If both the past and the external world exist only in the mind, and if the mind itself is controllable what then?"
My note. You get diameters like this for the universe in the BB model using the comoving radial distance from Earth for where the postulated CMBR is at with a redshift of about 1100 today. Commonly this is about 93-95 billion light years in diameter. Astronomers do not see this size at all and space there is expanding more than 3 x c velocity. As I pointed out in post #3, the universe age collapses too when using H0 = 73 km/s/Mpc compared to 67.
Albert Einstein had proposed his General Theory of Relativity at that time. One of the consequences of his theory is the prediction that space-time expands and contracts. In the presence of extremely concentrated mass, the theory predicts a contraction in space-time to the point of a singularity at the center of mass.
The black hole at the center of the Milky Way has such an extreme mass concentration. At 4 million solar masses crammed into a spherical volume with a radius of less than 13 million miles, this monster is crushing space-time both inside and outside its event horizon. Its gravitational impact combined with the gravitation of the rest of the stars in the galaxy cause a gradual contraction in the space-time of the entire galaxy. This is why space appears to expand while galaxies do not - galaxies contract.
We observe the universe from a contracting platform. When Hubble proposed his constant (H0), there was enough theoretical information to postulate that the observation of a constant expansion in the universe is the result of our own contraction and that the number H0 is a measure of that contraction.
If the physicists of the early 20th century had realized that, they would have saved a century of agonizing over the craziness observed in the universe, which is nothing more than the optical illusion produced by our own contraction.
There is no accelerating expansion, no dark energy. The calculated gravitation necessary to explain the movement of the universe that results in 96% being dark matter is a fiction. This is the agony of not realizing that we are observing an optical illusion in extra-galactic space-time resulting from our own contraction.
This nonsense as you have so aptly put it comes from one source. It is a simple question of galaxies being contracting structures. They contract from the gravitation in their black holes and from the mass in their stars. The Milky Way has a mass of 64 billion solar masses. This is the sum of the mass of Sagitarius A (its black hole) and all its stars. This mass produces an overall gravitation that results in the contraction of the space-time of the galaxy.
It is simple. We look out at space from a contracting structure and see an apparant expansion while the other contracting structures do not appear to expand. It is like looking at an expanding balloon with the individual items drawn on the ballon remaining constant. There can only be one explanation - galaxies contract.
When you realize that, all the nonsense goes away. There is no run away expansion, no dark energy pulling apart the universe, no movement so great that 96% of the universe must be dark matter to provide the required gravitation. This is a sensible universe behaving sensibly - no nonsense, just the Hubble constant (H0) measuring the rate of contraction of the Milky Way
How can we claim the universe is, and has been, accelerating but require it to always have one speed? What good is acceleration if nothing can go faster? I've yet to see an explanation for this simple question.
Also, the reason the Hubble Constant is now called the Hubble-Lemaitre Constant is because astronomers like to give credit where credit is due, but because of the remarkable clout and contributions from Hubble, the other two key players got set aside, apparently.
For those interested in the BBT story....
BBT Chronology:1912 -- Henrietta Swan Leavitt gives us the Cepheid variable law that allowed for galaxy distance determinations, necessary to find their expansion rates.
1912 -- September 17 Vesto Slipher found, with great effort, the first redshift data for galaxies (extragalactic nebulae).
1914 -- In a meeting of the American Astronomical Society, Slipher presented results for a total of 15 distant nebulae (later called galaxies). He was so convincing that his results were received by the audience (chronicles say) with a very long, standing ovation. Apparently, this is unusual.
George's Lemaitre was at that meeting.
1915-1916 GR (General Relativity) introduced by Einstein.
1917 – Einstein used GR to build a cosmology model.
1922 Alexander Friedmann found a math solution of Einstein’s equations suggesting the universe could be expanding or contracting. Einstein rejects this idea since the status quo was for a static universe.
DeSitter, and others, offered models that allowed for redshift in a static universe. DeSitter's model, for example, worked fine as long as his universe included no mass. :)
1927 -- Independent of Friedmann, Lemaitre, using GR, published (in French) his theory introducing not only the math for an expanding universe, but also evidence for this expansion (i.e. physics). His paper is entitled ‘Un Univers homogene de masse constante et de rayon croissant rendant compte de la vitesse radiale des n´ebuleuses extra-galactiques’. There's no evidence anybody every read this Belgium work. :)
In this paper, Lemaitre introduced the world's first estimate for an expansion rate for the universe. He used the redshift data from Slipher and the galaxy distances from Hubble. Combining these gives an approximate expansion rate.
In 1929, I think, he listened to Eddington claim there was no explanation for the redshifts. He translated his original paper and soon the prominent scientists had their explanation. But Hubble had greatly improved the data, so Lemaitre left out his cruder estimate for the expansion rate, opening the door further for Hubble to get credit, accidentally.
Einstein stated that his math was fine but his physics was "abominable".
Well said. Edwin Hubble always referred to the apparent expansion of the universe, he never committed to the fact the expansion was real. It was later on that apparent expansion became just expansion. People began to think of it as real. The alternative is that we are contracting and who would wish to contend with that.
In order to understand what is really out there, we must come to terms with our own contraction, which implies eventual disappearance to nothing. Ironically, what Saul Perlmutter et al were looking for in 1998 when they discovered the opposite was the big crunch. You have to look no further than our own Milky Way to find the so called big crunch.
This change of cosmological perspective leads to a new creation scenario - a big bang that is galactic not universal. That I would like to discuss at another time.
There are plenty of examples now published and reported. The cosmology calculators using GR and the FLRW metric show the age of the universe bounces all around too.