Russian physicists have carried out a numerical simulation of the formation of local structures from dark matter. This work applies to popular models of invisible matter such as axions and Fuzzy Dark Matter. Scientists have come to the conclusion that analogs of stars from dark matter can exist in our universe. A preprint with the results is published on the arXiv.org website.
Various astronomical observations do not agree with the assumption that the bulk of the mass in the universe is contained in luminous matter, such as stars, and the gas associated with them. At the moment, the most generally accepted explanation for this discrepancy is the hypothesis of dark matter, which assumes the existence of a substance transparent to electromagnetic interaction, which accounts for most of the mass. Such matter should form huge shells - halos - around galaxies. Theorists have proposed many models of dark matter, most of which describe it through not yet discovered elementary particles with different properties.
The new work examines the formation of stable local formations of dark matter, which retain themselves due to self-gravity, similar to ordinary stars. The article assumes that the particles of dark matter are bosons, and the resulting structures are accumulations of Bose-Einstein condensate, that is, the conclusions are valid for such popular models of invisible matter as axions and "blurred" dark matter. A feature of the work was modeling within the framework of a purely kinetic regime, without taking into account the interaction of dark matter particles with each other. For the first time, the authors were able to show that Bose stars can condense only due to gravity, no assumptions about the self-action of dark matter have to be made.
Axions were proposed by theoretical physicists as a solution to the problem of the observed violation of CP invariance (simultaneous replacement of all particles with antiparticles and mirror reflection of the system in space). They should have a low mass, weakly interact with known particles and decay into two photons. "Blurred" dark matter consists of particles of extremely small mass. It is so small that the corresponding de Broglie wavelength (the scale at which the quantum properties of the body are manifested) is comparable to the size of galaxies. In this case, it turns out that the particles are "smeared" in orbits around galaxies, just as electrons form clouds in atoms, and are not point particles in the orbits of nuclei.
The authors conclude that Bose stars from axions may well be born during the lifetime of the Universe, and their typical mass will be very small - they will be central objects in miniclusters with a mass of 10-13 solar masses. If they continue to accumulate particles, they can exceed the critical size and explode - such an event is a candidate for the role of a source of fast radio bursts. In the case of "diffuse" dark matter, such stars can also form in a relatively short time. Moreover, for a certain mass of such particles, this model solves the problem of the lack of dwarf satellites of large galaxies, such as the Milky Way: from numerical models it follows that our stellar system should have many tens of satellites, and much less is observed. If the theory of "blurry" dark matter is correct, then dwarf haloswhich were supposed to become the initial basis for small galaxies, have managed to condense into much smaller stars that are not able to hold a lot of ordinary matter around them. However, it should be noted that this theory is severely limited by other astronomical observations, so that only a small range of possible particle masses remains.