The findings, reached through a collaboration led by researchers from Japan’s Nagoya University, suggest that dark matter The early universe is less “clumpy” than many current cosmological models predict. If more work confirms this theory, it could change scientists’ understanding of how galaxies evolved and suggest that the basic rules governing the universe could have been different when it was 13.7 billion years old. Universe It was only 1.7 billion years old.
The key to mapping dark matter in the early universe is cosmic microwave background (CMB), a type of fossil radiation left over from the Big Bang scattered throughout the entire universe.
Masami Oshi is a professor at the University of Tokyo He said in a statement. “But after I gave a talk about a large, distant galaxy sample, Hironao came to me and said that it might be possible to look at the dark matter around these galaxies using the CMB.”
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Because light takes a finite amount of time to travel from distant objects to a land, astronomers see other galaxies as they existed when the observed light left them. The farther away a galaxy is, the longer the light travels to us, and thus the more distant we see in time, so we see the most distant galaxies as they were billions of years ago, in the infant universe.
It’s even more difficult to observe dark matter. Dark matter is the mysterious substance that makes up about 85% of the universe’s total mass. It does not interact with matter and light like the everyday matter made of protons and neutrons that fill stars, planets and us.
Early detection of dark matter
In order to “see” dark matter at all, astronomers must rely on its interaction with gravity.
according to Einstein’s theory of relativity, Objects of massive mass cause space-time curvature. A common analogy is an expandable rubber plate containing balls of increasing mass. The higher the mass, the more “bending” it causes in the sheet. Likewise, the larger the cosmic object, the greater the distortion of spacetime it causes.
Massive objects such as galaxies cause space-time to bend so severely that light from sources behind the galaxy is deflected, just as the path of marbles rolling through the stretched rubber sheet is deflected. This effect changes the location of the light source in the sky, a phenomenon called gravitational lensing.
To study the distribution of dark matter in A galaxy, astronomers can observe how the light from a source behind that galaxy changes as it passes through the lens galaxy. The more dark matter there is in the lensing galaxy, the more distorted the light passing through it.
But this technology has its limits.
Because the first and farthest galaxies are so faint, as astronomers look deeper into the universe and go back in time, the lensing effect becomes more subtle and harder to see, and scientists need a lot of background sources and a lot of early galaxies to spot the lens with dark matter. This problem has limited the mapping of the distribution of dark matter over galaxies between 8 and 10 billion years old.
But the CMB provides a light source older than any galaxy. CMB radiation is omnipresent radiation that arose when the universe cooled enough to allow atoms to form, reducing the number of free electrons scattered for a photon in a moment cosmologists call the “last scattering.” Allows reduction in free electrons Photons Traveling freely, which means that the universe suddenly stopped being opaque and became transparent to light.
And like light from other distant sources, the CMB can be distorted by dark matter galaxies due to gravitational lensing.
“Most researchers use source galaxies to measure the distribution of dark matter from the present to 8 billion years ago,” University of Tokyo associate professor Yuichi Harikan said in the statement. “However, we can look further into the past because we used the farthest CMB to measure dark matter.”
The team combined lens distortions from a large sample of ancient galaxies with those from the CMB to discover dark matter dating back to a time when the universe was only 1.7 billion years old. This ancient dark matter paints a very different cosmic picture.
“For the first time, we’ve been measuring dark matter from roughly the first moments of the universe,” Harrikan said. “12 billion years ago, things were very different. You see more galaxies that are forming than they are now; the first galaxy clusters are starting to form as well.”
These clusters can consist of anywhere from 100 to 1,000 galaxies bound together by large amounts of dark matter by gravity.
Is dark matter lumpy?
One of the most important aspects of the team’s findings is the possibility that dark matter was less lumpy in the early universe than many current models suggest.
For example, the widely accepted Lambda-CDM model suggests that small fluctuations in the CMB radiation should have triggered gravity creating packed pockets of matter. These fluctuations eventually cause matter to collapse to form galaxies, stars, and planets, and should also lead to dense pockets of dark matter.
“What we found is still uncertain,” Harrikan said. “But if true, it would suggest that the entire model is flawed as you go back in time. This is exciting because if the result persists after the uncertainties are reduced, it could indicate an improvement to the model that may provide insight into the nature of dark matter itself.”
The team will continue to collect data to assess whether the Lambda-CDM model is consistent with dark matter observations in the early universe or whether the assumptions behind the model need to be revised.
The data the team used to arrive at their findings originated from the Subaru Hyper Suprime-Cam survey, which analyzes data from a telescope in Hawaii. But the researchers have used only a third of this data so far, which means that a better distribution map of dark matter could be available where the rest of the observations are combined.
The team is also looking at data from Vera C Robin ObservatorySurveying Space-Time Inheritance (LSST), which could allow researchers to look at dark matter back in time.
“LSST will allow us to see half the sky,” Harrikan said. “I see no reason why we couldn’t see the distribution of dark matter 13 billion years ago then.”
The team’s research was published August 1 in the journal physical review messages.
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