Paul Kotlyar 08.09.2016, 15:20
V. Belokurov, D. Erkal, S. E. Koposov (IoA, Cambridge)
The Andromeda galaxy with the clumps of dark matter around
The Russian astronomers found a way to understand the nature of mysterious dark matter. How did you manage to catch the elusive essence of the tail that says “Газета.Ru”.
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An international team of astronomers from Cambridge University, which included two Russian researchers, found and successfully tested an elegant method of observing dark matter, which is able to shed light on the structure of this mysterious substance. Today, from the observations, astronomers know that dark matter in the Universe is very much —
it is more than 80% of the mass of the Universe, being invisible and manifesting itself solely by the gravitational interaction.
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That is the gravitational pull of dark matter indicates that the great mass of dark matter inside large galaxies. In the framework of today’s popular theory of cold dark matter it is assumed that in the early stages of the formation of the Universe dark matter coalesced, forming larger clots, they are at a certain stage began to fall ordinary matter, from which it was formed we see today galaxies and stars.
However, the theory predicts that beyond this Universe there should be more small pieces of dark matter, the so-called sub-halos with a mass of “only” thousands and millions of solar masses, whose effects on normal baryonic matter it is hard to notice because of their small mass.
And if the theory is correct, then inside each large clump of dark matter there must be many small, scattered also in the neighborhood of clot, in which there are no stars — kind of hierarchical structure.
Finding these small clots and engaged scientists, under the leadership of Denis Arkala from Cambridge, co-sponsored by Sergey Koposov and Vasily Belokurov (both graduates of the State astronomical Institute named after Sternberg).
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It turned out that the most convenient way to detect these invisible small clots is to monitor tidal flows, which remain in the destruction of globular star clusters orbiting our galaxy. Such clusters, groups of millions of gravitationally related to each other stars, rotating around our galaxy, at some point you start to lose stars
which stretched in a long and thin tail, with a width of several light years.
The beauty of these tails is that they are very sensitive to flying near gravitating objects that can easily ruin or break this stellar thread.
V. Belokurov, D. Erkal, S. E. Koposov (IoA, Cambridge)
The tidal tail. Blue — observed, green — calculated without disturbances, red — calculated perturbations
The photograph shows two gaps in the stream. One sharp, to the left of the cluster, and the second blurred and extended to the right. Thus the right of the gap exactly coincides in length with the previously predicted by calculations, that is, with high probability it was caused by flying past a clump of dark matter.
“In principle, left a gap may be caused not by dark matter, and the passage of giant molecular clouds in the disk of the galaxy — said Koposov. — But the hole on the right side is caused with a high probability it is the clump of dark matter as there is no such extended molecular clouds”.
These observations are consistent with the simulation of fracture in this cluster over the last 8 billion years. The animation shows how as the tidal destruction of a cluster in the sky, in length, and in the end breaks flying clumps of dark matter on small parts.
However, the main benefit from the findings — the ability to estimate the mass of flown clusters, and therefore to impose limits on the mass of the still undiscovered themselves of dark matter particles. The fact that the smaller the energy of these particles,
the less massive clumps of dark matter can form (fast particles it is difficult to hold around small masses).
“One way to understand the nature of dark matter is to determine the minimum size of structures that it forms. Still the smallest structures considered hundreds of millions of solar masses (dwarf galaxies), — said the astronomer. — Using stellar streams we can see the clots, the entire mass in millions of solar masses”.
Based on these observations, scientists have deduced a lower limit on the mass of the dark matter particle is 18 Kev.
