Scientists have conducted a new census of the amount of matter in the cosmos, finding that the stuff makes up 31% of our universe.
"To put that amount of matter in context, if all the matter in the universe were spread out evenly across space, it would correspond to an average mass density equal to only about six hydrogen atoms per cubic meter [about 35 cubic feet]," Mohamed Abdullah, a graduate student in the Department of Physics and Astronomy at the University of California, Riverside (UCR), said in a statement.
"However, since we know 80% of matter is actually dark matter, in reality, most of this matter consists not of hydrogen atoms but rather of a type of matter which cosmologists don’t yet understand," said Abdullah, who led a new study announcing the result.
Related: The history and structure of the universe (infographic)
The study, which was published online Friday (Sept. 25) in The Astrophysical Journal, suggests that 69% of the cosmos' matter-energy budget is dark energy, a mysterious force thought to be responsible for our universe's accelerating expansion.
That number is in rough agreement with previous estimates, which astronomers have calculated via a variety of methods. For example, the team behind Europe's Planck satellite, which scrutinized the cosmic microwave background — the glow left over from the Big Bang — determined in 2013 that dark energy makes up 68.3% of the universe.
The new study also reaffirms the piddling 5% contribution of "normal" matter, the stuff that makes up stars, planets, trees, oceans and everything else that we can directly see and touch.
Abdullah and his colleagues arrived at their number by studying galaxy clusters. The researchers developed a tool that measures a cluster's mass by examining the orbits of its member galaxies. They applied this tool to observations made by the Sloan Digital Sky Survey, a wide-ranging campaign that uses a telescope in New Mexico, creating a cluster catalog that the researchers then compared to numerical simulations.
Such comparison — observed cluster numbers and masses versus modeled predictions — is a proven technique for determining the universe's total matter content, the study team explained. That's because clusters, which take billions of years to form, are a sort of cosmological probe. Their observed numbers are sensitive to a number of variables, particularly the universe's total matter content.
"We have succeeded in making one of the most precise measurements ever made using the galaxy cluster technique," study co-author Gillian Wilson, a professor of physics and astronomy at UCR who leads the lab in which Abdullah works, said in the same statement.
"Moreover, this is the first use of the galaxy orbit technique, which has obtained a value in agreement with those obtained by teams who used noncluster techniques," such as the Planck researchers' cosmic microwave background method, she added.
Indeed, the 31% figure is a "best combined value," at which Abdullah and his team arrived after combining their cluster results with previous calculations performed using a variety of techniques, the researchers said.
Mike Wall is the author of "Out There" (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook.
it’s taking so long, it’s not fair.
They promised a basket of MACHO’s
a garland of WIMP’s, a gift of Axions
the last straw was neutrinos
at least we know baryons
Oh dear what can the matter be.
it’s taking so long it’s not fair
Of course they aren't going to measure the Big Crunch underneath; deepest inside hub; farthest outside rim. They aren't going to measure an infinitesimal-infinite. They can attempt to census the finitely relative local this side of breakdown, this side of collapse in horizon, but only in a fevered mind would someone attempt to measure the infinitely non-relative non-local inside that horizon / the other side of that horizon down and in, up and out.
Again, surface-wise, even across an infinity of finite universes, an average of 31% of the surface being matter would still seem just about right. Maybe even the perfect proportion.
"Because present-day galaxy clusters have formed from matter that has collapsed over billions of years under its own gravity, the number of clusters observed at the present time is very sensitive to cosmological conditions and, in particular, the total amount of matter. ... Finally, they compared the number of clusters in their new catalog with simulations to determine the total amount of matter in the universe.
"We have succeeded in making one of the most precise measurements ever made using the galaxy cluster technique," said coauthor Gillian Wilson, a professor of physics and astronomy at UCR in whose lab Abdullah works. "Moreover, this is the first use of the galaxy orbit technique which has obtained a value in agreement with those obtained by teams who used noncluster techniques such as cosmic microwave background anisotropies, baryon acoustic oscillations, Type Ia supernovae, or gravitational lensing.""
They measure matter density Ω_m and structure clustering parameter σ_8, and they fall on top of Planck (Ω_m) and BOSS (σ_8), with another factor 3 lowered uncertainty https://arxiv.org/abs/2002.11907 ].
Now they need to expand and check for robustness (especially since earlier similar methods did not do well), but meanwhile this is encouraging.
Thermal WIMPs seemed like such a slam dunk since that is presumably the way elementary particle are generated during the hot big bang and their mass and number range would fit dark matter. But that range has been eliminated by many observations by now .
Axions were always more of a solution looking for a problem - there are more promising ways to solve matter/antimatter asymmetry and thus the so called "strong CP problem", as was standard matter MACHOs, and both have been eliminated in direct searches and cosmological constraints .
So for whatever reason, the easier to detail non-gravitationally interacting dark matter doesn't seem to exist, and there will be a presumably much longer route to find out more on the dark matter we all know and love.
I think you mean energy content by volume (average energy density).
The universe will only continue to expand by the observed process - dark energy density suffice to ensure that.
Your comment reads like a stream-of-consciousness text, more so from this part on, so it is difficult to respond to.
Of course in any deceleration his universe would reverse from a steadily contracting universe to a steadily expanding universe (as he drops from plane of universe to plane of universe). And, likely, from many hydrogen atoms per cubic meter volume back to the very few as stated.
The universe traveler's relative 'local' universe is not the Earth's observers' relative 'local' universe. Separation in space-time results in separation of universes. Relativity will breakdown. What the Earth observer, astronomer, physicist, claims for the distant universe (u), or the Universe (U) at large, may not be what concerning the distant universe (or for the Universe at large). That figure of 31% average for matter just seems to me to be right for an average. My clumping it, producing an analogy to Earth's surface division between land surface and sea surface was just my analogy concerning "surface".
General relativity ensures that physics laws can be universal. The matter density is one such universal density parameter, since it is part of the general relativistic LCDM model that describes our universe.
Again, these comments are very hard to respond to.
This is a bit easier, since it reads as a combination of superstitions of philosophy and religion.
- The usual response to unrealistic models is that kicking a stone would convince anyone of reality. For simulation ideas specifically, there is also a problem of resolution (remember the recurring cat in Matrix?).
- Since 2018 we are fairly ensured that space is flat, and that we can therefore observe any activity of omnipotent (or large local) 'gods' against the zero energy density (and spontaneous expansion) of the universe. There is no such putative magic acting on the universe in its history, or acting now or can be in its future (since general relativity is self conssistent closed).
I don't see the relevance for our cosmology science - the models covers the local universe in detail and we may have good handle on the rest as well.
We can study the local universe many orders of magnitude of expansion into inflation before the later hot big bang (which, admittedly, isn't much in terms of time due to the high rate of expansion) .