The universe suppresses the growth of natural structures

The universe suppresses the growth of natural structures

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The artist’s sketch of the early universe slowly converges into the grand cosmic structure of the universe. Image credit: Minh Nguyen, University of Michigan and Thanh Nguyen (partner)

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The artist’s sketch of the early universe slowly converges into the grand cosmic structure of the universe. Image credit: Minh Nguyen, University of Michigan and Thanh Nguyen (partner)

As the universe evolves, scientists expect the vast universe to expand at a certain rate: dense regions such as star clusters will grow denser, while voids will grow empty.

But researchers at the University of Michigan have found that the speed at which these giant structures grow is slower than predicted by Einstein’s Theory of General Relativity.

They showed that as dark energy accelerates the expansion of the universe, the forced growth of the cosmic structure that the researchers see in their data is more prominent than theory predicts. Their results are published in the Physical review letters.

Galaxies are intertwined in the universe like the webs of a great cosmic spider. Their distribution is not unusual. Instead, they tend to cluster together. After all, the cosmic web as a whole began as small particles in the universe, which gradually grew into clusters of galaxies, and finally into clusters of galaxies and filaments.

“Every cosmic moment, a small clump of mass attracts and collects more and more matter from the region through gravitational interaction. As the region becomes harder and harder, it eventually collapses under gravity,” said Minh Nguyen, the lead author. research and postdoctoral research in the UM Department of Physics.

“So as they fall, the clumps grow denser. That’s what we’re talking about growing. It’s like a one-, two-dimensional weaving fabric where it’s like a sheet, a filament and a node. It’s a mixture of all three conditions, and you have galaxies that live along the fibers while galaxy clusters—groups of thousands of galaxies, the largest objects in our gravitationally bound universe—sit in their habitats.”

The universe is not made out of nothing. It may also contain a mysterious component called dark energy. Dark energy is accelerating the expansion of nature around the world. As dark energy accelerates the expansion of the universe, it has the opposite effect on large structures.

“If gravity acts as an amplifier that amplifies disruptive elements to grow into a larger structure, then dark energy acts as an attenuator that disrupts these disruptive elements and slows down the growth of the structure,” Nguyen said. “By studying how the cosmic structure has assembled and grown, we can try to understand the nature of mass and dark energy.”

Nguyen, MUM physics professor Dragan Huterer and UM graduate student Yuewei Wen examined the temporal growth of superstructure throughout cosmic time using several cosmological probes.

First, the team used what is called the cosmic microwave background. The cosmic microwave background, or CMB, is made up of photons emitted just after the Big Bang. These photons provide a picture of the early universe. As photons travel to our telescopes, their path can be distorted, or gravitationally lensed, by large structures in the path. By testing them, researchers can understand that the structure and matter between us and the cosmic microwave background is distributed.

Nguyen and his colleagues took the same opportunity with the weak gravitational lensing of galaxy shapes. The light from the background galaxy is distorted due to the gravitational interaction with foreground objects and galaxies. Cosmologists interpret these distortions to determine how matter is distributed.

“Of course, as the CMB and the background galaxy are located at a different distance from us and our telescopes, weak galaxy gravitational lensing often probes the distribution of objects at a later time compared to what is investigated by CMB weak gravitational lensing,” said Nguyen.

To see how it grew until later times, researchers also used galaxies in the universe. As galaxies fall into the gravitational wells of the underlying cosmic structures, their motions directly track the growth of the structure.

“The difference in the growth rates that we can achieve is becoming more and more apparent as we get closer to that date,” Nguyen said. “These probes are different individually and collectively they show growth suppression. Either we are missing some systematic errors in each of these probes, or we are missing new, late-time physics in our standard model.”

The results may address the so-called S8 tension in cosmology. S8 is a parameter that describes the growth of the structure. The tension arises when scientists use two different methods to determine the value of S8, and they disagree. The first method, using photons from the cosmic microwave background, shows a higher value of S8 than the value predicted from weak galaxy gravitational lensing and galaxy clustering measurements.

None of these probes measure construction growth today. Instead, they examine the situation in earlier periods, then extrapolate those measures to present time, assuming a common model. The cosmic microwave background probes the structure in the early universe, while the galaxy is weak in gravitational lensing and probes the formation of the universe.

The researchers’ findings of long-term growth suppression will bring the two S8 prices into perfect agreement, according to Nguyen.

“We were surprised by the significance of the abnormally high growth pressure numbers,” Huterer said. “Actually, I feel that the universe is trying to tell us something.

“We would like to further strengthen the statistical evidence of slowing growth. We would also like to understand the answer to the more difficult question of why the structures are growing faster than expected in the standard model with dark matter and dark energy. The reason for this The effect may be due to new properties of dark energy and dark matter, or another extension It’s a General Relationship and a common model that we haven’t even thought about yet.”

More information:
Nhat-Minh Nguyen et al, Evidence for Reduced Growth Structure in the Concordance Cosmological Model, Physical review letters (2023). DOI: 10.1103/PhysRevLett.131.111001

Journal information:
Physical review letters

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