Scientists reveal distribution of dark matter around galaxies 12 billion years ago -- further back in time than ever before

More than ever before, a scientific cooperation led by researchers at Nagoya University in Japan examined the characteristics of dark matter around galaxies as they appeared 12 billion years ago. Their research, which was published in Physical Review Letters, raises the intriguing idea that when analyzing the early history of our universe, the basic cosmological laws may vary.

It's difficult to remember something that happened so long ago. We observe distant galaxies not as they are today but as they were billions of years ago due to the limited speed of light. Observing dark matter, which does not emit light, is considerably more difficult.

Consider a faraway source galaxy that is even more remote than the target galaxy for studying its dark matter. As predicted by Einstein's theory of general relativity, the gravitational attraction of the foreground galaxy, including its dark matter, alters the surrounding space and time. The apparent form of the galaxy is altered as a result of the light from the source galaxy bending as it passes through the distortion. The distortion increases with the amount of dark matter. Because of the distortion, researchers can calculate the quantity of dark matter in the vicinity of the foreground galaxy (also known as the "lens" galaxy).

But at a certain threshold, scientists get into trouble. In the furthest regions of the cosmos, galaxies are exceedingly dim. As a result, this strategy gets less successful as we look farther away from Earth. There must be a large number of background galaxies in order to identify the signal because the lensing distortion is typically modest and challenging to detect.

The majority of earlier investigations stayed within the same parameters. They could only investigate dark matter from a time period of no more than 8–10 billion years ago due to their inability to find enough distant source galaxies to assess the distortion. The question of how dark matter was distributed between now and 13.7 billion years ago, at the beginning of our universe, was left unanswered by these restrictions.

A research team led by Hironao Miyatake from Nagoya University, in association with the University of Tokyo, the National Astronomical Observatory of Japan, and Princeton University, overcame these difficulties and observed dark matter from the farthest reaches of the universe by using a different source of background light, the microwaves released from the Big Bang itself.

First, the researchers chose 1.5 million lens galaxies that should have been visible 12 billion years ago based on data from the Subaru Hyper Suprime-Cam Survey (HSC) observations.

They then used microwaves from the cosmic microwave background (CMB), the radiation leftover from the Big Bang, to overcome the lack of galaxy light even further out. The scientists analyzed how the dark matter surrounding the lens galaxies affected microwaves seen by the European Space Agency's Planck spacecraft.

The majority of the observations were performed by Professor Masami Ouchi of the University of Tokyo. He said, "Look at dark matter orbiting distant galaxies." "It was an absurd notion. Nobody knew we could pull this off. However, Hironao approached me after I delivered a presentation about a sizable sample of far-off galaxies and suggested that it would be feasible to use the CMB to look at the dark matter around these galaxies."

Yuichi Harikane, assistant professor at the University of Tokyo's Institute for Cosmic Ray Research, further said that "the majority of researchers employ source galaxies to measure the dispersion of dark matter from the present to eight billion years ago." "However, since we measured dark matter using the more distant CMB, we could go further back in time. We were measuring dark matter for the first time nearly from the beginning of the cosmos."

The scientists quickly discovered they had a sizable sample to identify the spread of dark matter after doing a preliminary investigation. They found dark matter 12 billion years in the past by combining the enormous sample of far-off galaxies and the lensing distortions in CMB. These galaxies are visible barely 1.7 billion years after the universe's creation, indicating that they were produced recently.

I was glad that we were able to provide a fresh look at that time period, Miyatake stated. "Things were considerably different 12 billion years ago. More young galaxies are visible than at the moment, and the first galaxy clusters are also beginning to emerge." Galaxy clusters are made up of 100–1000 galaxies that are gravitationally linked and have a lot of dark matter.

According to Neta Bahcall, the Eugene Higgins Professor of Astronomy, Professor of Astrophysical Sciences, and Director of Undergraduate Studies at Princeton University, "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 with time."

The clumpiness of dark matter was one of the researchers' most intriguing discoveries. The Lambda-CDM model, the accepted explanation of cosmology, states that minute variations in the CMB attract nearby matter by gravity to produce pools of densely packed matter. In these crowded areas, this leads to inhomogeneous aggregates that eventually give rise to stars and galaxies. According to the group's findings, their clumpiness measurement was less than what the Lambda-CDM model anticipated.

Miyatake is excited about the potential. He stated, "Our conclusion is still tentative. "However, if it is accurate, it would imply that if you went further back in time, the entire concept is incorrect. This is intriguing because, if the conclusion persists once the uncertainties are minimized, it would point to a model upgrade that could shed light on the characteristics of dark matter."

Andrés Plazas Malagón, an associate research fellow at Princeton University, said, "At this point, we will strive to acquire better evidence to evaluate if the Lambda-CDM model is indeed able to describe the observations that we have in the universe." And as a result, it could be necessary to review the model's underlying assumptions.

"Large-scale surveys, like the ones utilized in this work, have the advantage of allowing for the study of everything visible in the resultant photographs, from close asteroids in our solar system to the most distant galaxies from the early cosmos. You may investigate a variety of different problems using the same data, "Michael Strauss, a professor at Princeton University and the department's chair, made this statement.

Data from currently operational telescopes, such as Planck and Subaru, were utilised in this investigation. Only a third of the Subaru Hyper Suprime-Cam Survey data has been examined by the organization. The analysis of the complete data set will come next, which should provide a more accurate determination of the distribution of dark matter. The group intends to investigate more of the earliest regions of space in the future using a sophisticated data collection, such as the Legacy Survey of Space and Time (LSST) from the Vera C. Rubin Observatory. According to Harikane, LSST will let us to view half the sky. There is no reason, in my opinion, why we couldn't see the dispersion of dark matter 13 billion years ago.

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