Scientists have made one of the most accurate maps of matter in the universe, and it shows that something may be missing from our best model of the cosmos.
Created by combining data from two telescopes observing different types of light, the new map revealed that the universe is less “clumpy” than previous models predicted, a potential sign that the vast cosmic web connecting galaxies is less well known than scientists thought.
According to our current understanding, the cosmic web is a gigantic network of crisscrossing celestial superhighways paved with hydrogen gas and dark matter. Taking shape in the chaotic aftermath of the big Bang, the tendrils of the net formed like clumps of the turbulent broth of the young universe; where multiple strands of the web intersected, galaxies eventually formed. But the new map, published on January 31 as Three (opens in a new tab) separated (opens in a new tab) studies (opens in a new tab) in Physical Review D, shows that in many parts of the universe, matter is less clumped together and more evenly distributed than theory predicts it should be.
Related: How dark is the cosmic web?
“It appears that there are slightly fewer fluctuations in the universe today than we would predict assuming our standard cosmological model is anchored to the early universe,” said co-author Eric Baxter, an astrophysicist at the University of Hawaii. said in a statement (opens in a new tab).
Spinning the cosmic web
According to the standard model of cosmology, the universe began to take shape after the Big Bang, when the young cosmos filled with particles of matter and antimatter, which appeared only to annihilate each other on contact. Most of the building blocks of the universe vanished in this way, but the rapid expansion of the fabric of spacetime, coupled with some quantum fluctuations, meant that a few pockets of primordial plasma survived here and there.
the force of gravity they soon compressed these pockets of plasma in on themselves, heating the matter as it came together to such an extent that sound waves traveling at half the speed of light (called baryon acoustic oscillations) spread outward from the clumps. of plasma. These waves pushed matter that had not yet been drawn toward the center of a clump, where it settled as a halo around it. At that time, most of the matter in the universe was distributed as a series of thin films that surrounded countless cosmic voids, like a nest of soap bubbles in a kitchen sink.
Once this matter, mainly hydrogen and helium, cooled enough, it coagulated further to give rise to the first stars, which, in turn, forged heavier and heavier elements through nuclear fusion.
To map how the cosmic web was woven, the researchers combined observations taken with the Dark Energy Survey in Chile, which scanned the sky in near-ultraviolet, visible, and near-infrared frequencies from 2013 to 2019, and the South Pole Telescope. . which is located in Antarctica and studies the microwave emissions that make up the cosmic microwave background, the oldest light in the universe.
Although they look at different wavelengths of light, both telescopes use a technique called gravitational lensing to map the buildup of matter. Gravitational lensing occurs when a massive object comes between our telescopes and its source; the more distorted the light from a given pocket of space appears, the more matter there is in that space. This makes gravitational lensing an excellent tool for tracking both normal matter and its mysterious cousin, dark matter, which, despite making up 85% of the universe, does not interact with light except by distorting it with gravity.
Using this approach, the researchers used data from both telescopes to pinpoint the location of the matter and debug the data set from one telescope by comparing it to the other.
“It works as a cross check, so it becomes a much more robust measure than if you just used one or the other,” co-senior author Chihway Chang (opens in a new tab)astrophysicist at the University of Chicago, said in the statement.
The cosmic matter map the researchers produced fit our understanding of how the universe evolved perfectly, except for one key discrepancy: It was more evenly distributed and less clumped than the standard model of cosmology would suggest.
There are two possibilities to explain this discrepancy. The first is that we are simply looking at the universe too imprecisely, and that the apparent deviation from the pattern will disappear as we get better tools to observe the cosmos. The second, and more important, possibility is that our cosmological model is missing some really important physics. Finding out which is the real one will require more cross-surveying and mapping, as well as a deeper understanding of the cosmological constraints that bind the soap scum of the universe together.
“There is no known physical explanation for this discrepancy,” the researchers wrote in one of the studies. “Cross-correlations between surveys…will allow for significantly more powerful cross-correlation studies that will offer some of the most accurate and precise cosmological constraints, and that will allow us to continue to test the stress of the [standard cosmological] model.”
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