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Study of dark matter from 12 billion years ago sheds light on the theory of cosmology

A team of researchers analyzed the nature of dark matter and galaxies from 12 billion years ago by using light from the Big Bang. Their discoveries may disprove some aspects of Einstein’s general theory of relativity, which is the backbone of the theory of cosmology.

(CN) — The nature of dark matter surrounding galaxies 12 billion years ago, which is the furthest back by far that scientists have ever had the capability to go, is the subject of a collaborative study published Monday by researchers at Nagoya University in Japan.

The team’s findings, published in the journal Physical Review Letters, rely in part on the researchers’ ability to use light from the Big Bang 13.7 billion years ago to help describe what exists around the galaxies due to the properties of the speed of light.

They conclude in their findings that traditional theories of cosmology, which are largely defined by Einstein’s general theory of relativity, might not apply as well to the earliest era of our universe.

Because of the laws of the speed of light, when we look into the sky, we are not seeing the galaxy as it presently is but as it was billions of years ago. But to see the galaxy or the nature of dark matter prior to 10 or so billion years ago is difficult because distant galaxies are incredibly faint, not giving enough light for the purpose of analyzing form.

This has left many unanswered questions about the distribution of dark matter between roughly 10 billion and 13.7 billion years ago when a spontaneous combustion in an otherwise cold and empty place instantly affected an ever-expansion of matter following the Big Bang.

For this study, scientists were able to harness microwave light from the Big Bang and use it to analyze galaxies from what, relatively speaking at least, was soon after that phenomenon which many astrophysicists agree began our universe by literally setting it in motion.

“Most researchers use source galaxies to measure dark matter distribution from the present to eight billion years ago," assistant professor Yuichi Harikane of the Institute for Cosmic Ray Research, University of Tokyo explained in a press release.

“However, we could look further back into the past because we used the more distant CMB [cosmic microwave background] to measure dark matter. For the first time, we were measuring dark matter from almost the earliest moments of the universe.” 

Dark matter, which many astrophysicists believe comprises at least 80% of the matter and energy making up our galaxy, cannot be “sensed” with conventional instruments and has long intrigued researchers in that it appears to influence gravity but does not interact with light.

Dark matter distorts the space around it for scientists attempting to observe a galaxy because when light travels through dark matter it bends, changing the apparent shape of the galaxy and distorting both space and time, just as Einstein predicted in his general theory of relativity.

The more dark matter surrounding a galaxy, the more distortion there is on the surrounding space. Thus, scientists typically help define a galaxy by measuring the amount of dark matter surrounding galaxies in the distant foreground.

Rather than studying the nature of dark matter by measuring the incredibly faint and distorted light from distant galaxies this time, however, a research team led by Hironao Miyatake from Nagoya University, together with the University of Tokyo, the National Astronomical Observatory of Japan and Princeton University, used the light from microwaves from the cosmic microwave background (CMB) which are radiation residue from the Big Bang.

The team collected data from observations made by the Subaru Hyper Suprime-Cam Survey (HSC) to identify 1.5 million lens galaxies 12 billion years ago.  

“Look at dark matter around distant galaxies?” Masami Ouchi of the University of Tokyo, who made many of the observations asked in a press release. “It was a crazy idea. No one realized we could do this. But after I gave a talk about a large distant galaxy sample, Hironao came to me and said it may be possible to look at dark matter around these galaxies with the CMB.”  

The dark matter observed in the team’s research is only 1.7 billion years more recent than the beginning of the universe, thereby in terms of relativity the galaxies they were able to study using CMB are considered basically just formed.

“I was happy that we opened a new window into that era,” Miyatake said in the press release.

"12 billion years ago, things were very different. You see more galaxies that are in the process of formation than at the present; the first galaxy clusters are starting to form as well.”

Galaxy clusters contain between 100 and 1,000 galaxies held together with gravity and copious 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 with time,” Neta Bahcall, Eugene Higgins professor of Astronomy, professor of astrophysical sciences, and director of undergraduate studies at Princeton University said in the press release.

One highlight of the team’s research has to do with the “clumpiness” of dark matter, or its composition. By the standard theory of cosmology, known as the Lambda-CDM model, the density of the dark matter should have been greater. The Lambda-CDM model predicts that minor fluctuations in the CMB creates ponds of extremely dense matter that in turn forms stars and galaxies.

“Our finding is still uncertain”, Miyatae said. “But if it is true, it would suggest that the entire model is flawed as you go further back in time. This is exciting because if the result holds after the uncertainties are reduced, it could suggest an improvement of the model that may provide insight into the nature of dark matter itself.” 

Andrés Plazas Malagón, associate research scholar at Princeton University, agreed.

“At this point, we will try to get better data to see if the Lambda-CDM model is actually able to explain the observations that we have in the universe,” Plazas Malagón said in the press release. “And the consequence may be that we need to revisit the assumptions that went into this model.” 

This study is just a preliminary step among many using data available from existing telescopes and at this point the team has only reviewed about a third of the Subaru Hyper Suprime-Cam Survey data.

Next will be an analysis of the entire data set, which is certain to lead to additional discoveries.

“I don’t see any reason we couldn’t see the dark matter distribution 13 billion years ago next,”  Harikane said in the release.

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