Scientists have revealed the distribution of dark matter around galaxies 12 billion years ago

Scientists have revealed the distribution of dark matter around galaxies 12 billion years ago, more time ago than ever before

Radiation remnants from the Big Bang, distorted by dark matter 12 billion years ago. Credit: Rikko Matsushita

A collaboration led by scientists at Nagoya University in Japan has investigated the nature of dark matter surrounding galaxies seen 12 billion years ago, billions of years ago. Their findings, published in physical review messagesoffers the tantalizing possibility that the basic rules of cosmology may differ when studying the early history of our universe.

It’s hard to see something that happened so long ago. Because of the limited speed of light, far galaxies It does not appear as it is today, but as it was billions of years ago. But the most difficult thing is to watch dark matterwhich does not emit light.

Think of a galaxy with a distant source, far beyond the galaxy in which one wants to search its dark matter. The gravitational pull of the foreground galaxy, including its dark matter, distorts surrounding space and time, as predicted by Einstein’s theory of general relativity. When light from the source galaxy travels through this distortion, it bends, changing the galaxy’s apparent shape. The greater the amount of dark matter, the greater the distortion. Thus, scientists can measure the amount of dark matter around the foreground galaxy (the “lens” galaxy) of distortion.

However, after a certain point scientists are faced with a problem. Galaxies in the depths of the universe are incredibly faint. As a result, the further away from Earth, the less effective this technique becomes. Lens distortion is subtle and difficult to detect in most cases, so several background galaxies are necessary for signal detection.

Most previous studies have stuck to the same bounds. Because they could not detect source galaxies far enough away to measure the distortion, they could only analyze dark matter no more than 8-10 billion years ago. These limitations left open the question of the distribution of dark matter between this time and 13.7 billion years, around the beginning of our universe.

To overcome these challenges and observe dark matter from the most distant regions of the universe, a research team led by Hironao Miyatake of Nagoya University, in collaboration with the University of Tokyo, the National Astronomical Observatory of Japan, and Princeton University, used a different source. From the background light, microwaves were released from the Big Bang itself.

First, using data from observations from the Subaru Hyper Suprime-Cam Survey (HSC), the team identified 1.5 million lens galaxies using visible light, which were selected to view 12 billion years ago.

Then, to overcome the lack of galactic light far away, they used microwaves from cosmic microwave background (CMB), the radiation leftover from the Big Bang. Using microwaves detected by the European Space Agency’s Planck satellite, the team measured how dark matter around lens galaxies distorts microwaves.

“Look at the dark matter around distant galaxies?” Professor Masami Oshi of the University of Tokyo, who made several observations, asked. “It was a crazy idea. Nobody realized we could do this. But after I gave a talk about a large, distant galaxy sample, Hironao came to me and said it might be possible to look at the dark matter around these galaxies using the CMB.”

“Most researchers use source galaxies to measure the distribution of dark matter from the present to eight billion years ago,” added Associate Professor Yuichi Harikan of the University of Tokyo’s Cosmic Ray Research Institute. “However, we can look further into the past because we used the farthest CMB to measure dark matter. For the first time, we’ve been measuring dark matter from roughly the very first moments of the universe.”

After an initial analysis, the researchers quickly realized that they had a sample large enough to detect the distribution of dark matter. By combining a large distant galaxy sample with lens anomalies in the CMB, they discovered dark matter a very long time ago, 12 billion years ago. That’s only 1.7 billion years after the universe began, and so these galaxies are seen soon after they first formed.

“I was glad that we opened a new window on that era,” said Miyatake. “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.” Galactic clusters consist of 100-1000 gravitationally bound galaxies with large amounts of dark matter.

“This result gives a very consistent picture of galaxies and their evolution, as well as the dark matter in and around galaxies, and how this picture evolves over time,” said Nita Bahkal, Eugene Higgins Professor of Astronomy, and Professor of Astrophysics. Director of Undergraduate Studies at Princeton University.

One of the researchers’ most exciting findings was related to dark matter agglomeration. According to the standard theory of cosmology, the Lambda-CDM model, minute fluctuations in the CMB form pools of densely packed matter by attracting surrounding matter through gravity. This creates heterogeneous masses that form stars and galaxies in these dense regions. The group’s results indicate that the agglomeration measure was lower than what the Lambda-CDM model predicted.

Miyatake is excited about the possibilities. “What we found is still uncertain,” he said. “But if true, it suggests 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.”

“At this point, we will try to get better data to see if the Lambda-CDM model is actually able to explain the observations we have in the universe,” said Andrés Plazas Malagón, a research associate at Princeton University. “The result may be that we need to reconsider the assumptions that went into this model.”

“One of the strengths of looking at the universe with large-scale surveys, such as the one used in this research, is that you can study everything you see in the resulting images, from nearby asteroids in our solar system to the most distant ones,” said Michael Strauss, professor and chair of the Department of Astrophysics. At Princeton University, galaxies are from the very beginning of the universe.You can use the same data to explore a lot of new questions.

This study used available data from existing telescopes, including Planck and Subaru. The group reviewed a third of Subaru Hyper Suprime-Cam survey data. The next step will be to analyze the entire data set, allowing for a more accurate measurement of the dark matter distribution. In the future, the team expects to use an advanced data set such as the Vera Sea-Robin Observatory Space-Time Legacy Survey (LSST) to explore more early parts of space. “LSST will allow us to see half the sky,” Harrikan said. “I see no reason why we can’t see the darkness issue distribution before the next 13 billion years.”


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more information:
First definition of a CMB lens signal produced by 1.5 million galaxies at z∼4: Constraints on fluctuations in matter density at high redshift, arXiv: 2103.15862 [astro-ph.CO] arxiv.org/abs/2103.15862 accepted by PRL: Journal.aps.org/prl/accepted/… 052a720dad1051463b2c

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Nagoya University


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