A mammoth effort by a huge international team of scientists has just given us the most accurate map of all matter in the Universe to date.
By combining data from two major studies, the international collaboration has revealed where the Universe does and does not store all its junk, not just the normal stuff that makes up planets, stars, dust, black holesgalaxies, but the dark matterAlso: the mysterious invisible mass that generates more gravity than normal matter can account for.
The resulting map, which shows where matter has congregated over the Universe’s 13.8 billion-year lifetime, will be a valuable reference for scientists seeking to understand how the Universe evolved.
In fact, the results already show that the issue isn’t distributed exactly as we thought it was, which suggests that there might be something missing from the current one. standard model of cosmology.
According to current models, at the point of big Bang, all matter in the Universe condensed into a singularity: a single point of infinite density and extreme heat that suddenly exploded, spewing out quarks that quickly combined to form a soup of protons, neutrons, and nuclei. Hydrogen and helium atoms arrived a few hundred thousand years later; of them the whole Universe was made.
How these early atoms scattered, cooled, clumped together, formed stars, rocks, and dust is detective work based on what the Universe around us looks like today. And one of the main clues that we’ve used is where the whole thing is now, because scientists can then work backwards to figure out how it got there.
But we can’t see everything. In fact, most of the matter in the Universe, about 75 percent, is completely invisible to our current detection methods.
We’ve only detected it indirectly, because it creates stronger gravitational fields than there should be just based on the amount of normal matter. This manifests itself in such phenomena as galaxies spinning faster than they should, and a little quirk of the Universe we call gravitational lensing.
When something in the Universe has enough mass, say a cluster of thousands of galaxies, the gravitational field around it becomes strong enough to influence the curvature of spacetime itself.
That means that any light that travels through that region of space travels along a curved path, resulting in distorted and magnified light. These lenses are also stronger than they should be if they were just created by normal matter.
To map the matter in the Universe, the researchers compared gravitational lensing data collected by two different studies: the dark energy survey, which collected data at near-ultraviolet, visible, and near-infrared wavelengths; and the South Pole Telescopewhich collects data on the microwave cosmic backgroundthe faint traces of radiation left over from the Big Bang.
By comparing these two data sets taken by two different instruments, researchers can be much more confident in their results.
“It works as a cross check, so it becomes a much stronger measure than if you just used one or the other.” says astrophysicist Chihway Chang from the University of Chicago, who was lead author of one of three papers describing the work.
The main authors of the other two articles are physical Yuki Omori from the Kavli Institute for Cosmological Physics and the University of Chicago, and a telescope scientist Tim Abbott of the Cerro Tololo Inter-American Observatory of NOIRLab.
The resulting map, based on the positions of the galaxies, the lensing of the galaxies, and the lensing of the cosmic microwave background, can be extrapolated to infer the distribution of matter in the Universe.
This map can then be compared to models and simulations of the evolution of the Universe to see if the observed matter distribution matches theory.
The researchers ran some comparisons and found that their map was a mostly consistent match with current models. But not quite. There were some very slight differences between the observation and the prediction; the distribution of matter, the researchers found, is less lumpy, more evenly spaced than models predict.
This suggests that our cosmological models might need some adjustment.
That’s not really a surprise: there are some mismatches between cosmological observation and theory that seem to suggest we’re missing a trick or two, somewhere; and the team’s findings are consistent with previous work, but the more accurate and complete our data, the more likely we are to resolve these discrepancies.
There is more work to be done; the findings are not yet certain. Adding more surveys will help refine the map and validate (or overturn) the team’s findings.
And, of course, the map itself will help other scientists conduct their own investigations into the mysterious and murky history of the Universe.
The research has been published in Physical review D. All three documents are available on the arXiv preprint server and can be found here, hereY here.
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