The mode of cosmological evolution of dark matter is the same as that of visible matter

Large structures in the universe that are composed of dark matter develop in a similar way to large structures that are based on visible matter. This is one of the important conclusions derived from a new computer simulation. The calculation of the simulation is a meeting point in many years of work by a team of Polish, German and Russian astrophysicists and cosmologists

Large structures in the universe that are composed of dark matter develop in a similar way to large structures that are based on visible matter. This is one of the important conclusions derived from a new computer simulation. The calculation of the simulation is a meeting point in many years of work by a team of Polish, German and Russian astrophysicists and cosmologists.

A team of scientists from the Faculty of Physics, University of Warsaw (FUW), the Lebedev Physical Institute of the Russian Academy of Sciences and the Institute for Astrophysics in Potsdam ), prepared a high-resolution simulation. With the help of the simulation, it is possible to trace the development of clouds of dark matter and visible matter that fill the universe. The results confirm previous assumptions concerning the basic properties of dark matter, especially its distribution on a cosmological scale.

Astronomers have struggled with explanations for the motion of stars within galaxies and the motion of galaxies in galaxy clusters. Measurements have shown that a typical galaxy contains 10 to 50 times more dark matter than visible matter, and that galaxy clusters contain even 100 to 500 times more dark matter than visible matter. "It seems that visible matter, which makes up our everyday world, is nothing more than a slight addition to dark matter. There is at least six times as much dark matter in the universe, and no one knows what it is. Discovering its nature [of dark matter, a.a.] is an exciting experience," says Professor Marek Demiański, from the Faculty of Physics at the University of Warsaw.

Currently, it is assumed that dark matter consists of exotic particles that are not yet known to science, and that interact minimally, if at all, with electromagnetic radiation and particles that are familiar to us today. Scientists can observe dark matter particles by indirect methods only, for example by investigating the effect of dark matter gravity on the movement of visible matter in the universe.
Given the significant amount, it is assumed that dark matter played a key role in the formation of galaxies and their clusters. Therefore, scientists are interested in the way dark matter is distributed in the universe, and how the structures that store it have evolved over time. To answer these questions, it is necessary to observe galaxy clusters, whose light travels on its journey to Earth for ten billion years or more. However, distant objects are difficult to detect. Therefore, the amount of dark matter observations is not sufficient for statistical research.
Computer simulations are effective in studying dark matter. They make it possible to observe the formation process in dark matter clusters on a large scale, and its effect on the spatial distribution of normal matter. By comparing the results obtained in this way with observational evidence, it is possible to assess the truth of the scientists' hypotheses regarding the properties of dark matter.

In the early period after the Big Bang, dark and visible matter were more or less evenly distributed in the universe. Unlike visible matter, dark matter does not interact with electromagnetic radiation, which filled the universe shortly after the Big Bang, and therefore succumbs to its own gravity more quickly. Slight distortions in the distribution of dark matter began to gravitationally contract, pulling in dark matter, and then visible matter as well. The simulation by the international team shows this process.

During the simulation, scientists analyzed the behavior of about a billion point objects inside a cube, the length of each of whose faces is several hundred million light years. Over time, the dots spread out as the universe ballooned. The billion points were evenly distributed in the cube, and their number was determined only by the limit of the settlement capabilities of modern computers. Each point in the simulation had a mass of one hundred million suns. Dark matter properties were given to most points. The scientists then analyzed how the distribution of points changed over time, under the influence of gravity.

One of the most important conclusions from the simulation is the confirmation of self-identity between the evolution processes of dark matter structures and visible matter structures on a cosmological scale. It means, if we examine a cube four billion years after the big bang, and compare it to a cube ten billion years old, then, after adjusting the dimensions of the two cubes, the structures of visible and dark matter will be almost identical.

"This identity between the development processes of the two types allows us to reconstruct the distribution of dark matter on the basis of the distribution of visible matter. Our simulation confirmed this effect and we can say with greater certainty that we can gain insight into the invisible world of dark matter by observing the movement of visible matter," concludes Professor Damianansky.
The results of the simulation were published in the Monthly Notices of the Royal Astronomical Society, and were presented at the international conference JENAM 2011 European Week of Astronomy and Space Science last July, in St. Petersburg, Russia.

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