New research at the University of Sussex has for the first time simulated dark matter in a new way and disturbed conventional thinking about the composition of the universe. The study, published yesterday, October 2, 2019, in Physical Review Letters was co-authored with Princeton, Harvard, Cambridge, and MIT universities and others.
Scientists have long suspected a lot of the universe is made up of invisible particles or dark matter, and they have to be very cold and heavy. The search for evidence, however, was difficult and led researchers to consider alternative theories.
The new simulations show how stars and galaxies could have formed and clustered at the origin of the universe when dark matter is not very light. Very hard, as most scientists have assumed.
A University of Sussex physicist worked with an international team to calculate how dark matter behaves and how early galaxies would have looked if they had been "blurry" and extremely light in mass.  The theory of "blurred" dark matter suggests that the dark matter is made up of tiny particles that are so bright that they behave like quantum matter and move in waves. Its quantum nature can be seen on galactic scales. Traditionally, it has been assumed that dark matter is cold (ie where the particles do not move). However, doubts have arisen around this theory because particle accelerators have so far been unable to produce such a dark matter. The new theory of "fuzzy dark matter" has gained in popularity because, according to particle physics, it makes sense, but has never been completely simulated.
The simulations show that galaxies would have taken shape at the beginning of the universe if the dark matter had been blurry and extremely bright. The team juxtaposes them with the known galaxies formed in the cold dark matter scenario. As the universe has aged, galaxies have changed their shape. But with the advent of the new generation of telescopes – including the James Webb Space Telescope, where Sussex physicists work – scientists expect to be able to look back at the history of the universe to see how it used to look.  Anastasia Fialkov, who conducted the research at the University of Sussex, said:
"The nature of dark matter is still a mystery. The fuzzy theory of dark matter makes sense in terms of fundamental physics, such as string theory, and is therefore an interesting candidate for dark matter. And when the fuzzy theory of dark matter is proven by the new generation of powerful telescopes, we have pinpointed the nature of dark matter: one of the greatest secrets of all.
"Researchers around the world are searching for darkness matter and particle physicists are building models of dark matter, and many of them have assumed that dark matter is" cold ". The dark matter fuzzy theory, in which dark matter behaves like a wave on galactic scales, now offers a credible alternative scenario: dark matter is tiny and moves in waves that behave like quantum matter. Our simulations are the first to deal with the formation of galaxies in the context of fuzzy dark matter.
Professor Kathy Romer, astrophysicist at the Faculty of Mathematics and Physics at the University of Sussex, said:
"The hunt for dark matter is a bit like" Where's Wally? ". The dedicated work of astronomers and particle physicists in recent decades has given us some of the clues we need to look for to match Wally's striped sweater and hat, but we still have not found him. Maybe we should not have searched for Wally (cold dark matter) all the time, but for Wenda (fuzzy dark matter). This new research is so important because it gives us another clue to look for, much like Wenda's striped socks. "
Philip Mocz, Einstein Fellow at Princeton, says:
" Dark matter is a kind of cradle where galaxies are born and the cradles shape galaxies. Different models of dark matter predict different forms of cradles, especially in the young universe. It's a great place to search for Dark Matter and get new clues. "
What do the researches show?
The researchers found that galaxies formed in the early universe when the dark matter was cold almost spherical "halos". If dark matter were blurred, the early universe would have looked different, with galaxies first forming in extended tails or "filaments." And the size, shape, and fragmentation of these filaments vary in each scenario.
The cold dark matter hypothesis works well to describe the large-scale structure of the observable universe. Therefore, most models of galaxy formation are based on the assumption that dark matter is cold. However, there are discrepancies between observations and predictions of cold dark matter. If you look at very small galaxies, the distribution of dark matter does not match the predictions of theoretical models. Because particle accelerators have not yet discovered dark matter, the model of cold dark matter is becoming less and less attractive.
The team developed the first realistic predictions of how early galaxies might have looked in a universe dominated by fuzzy dark matter. The goal is to provide a map for future telescopes, such as the James Webb Space Telescope, which may look far enough back in time to detect the earliest galaxies. If they see galaxies with the tails or "filaments" simulated in this study, this could confirm that dark matter is naturally blurred.
Dr. Fialkov has now moved to the University of Cambridge.
"First star-forming structures in flaky cosmic filaments" by Philip Mocz, Anastasia Fialkov, Mark Vogelsberger, Fernando Becerra, Mustafa A. Amin, Sownak Bose, Lars Hernquist, Pierre-Henri Chavanis, Lachlan Lancaster, Federico Marinacci, Victor H. Robles and Jesús Zavala, October 2, 2019, Physical Review Letters .
DOI: 10.1103 / PhysRevLett.123.141301