Astronomers at the University of California, Riverside have uncovered why some dwarf galaxies are completely deprived of dark matter, although previously invisible matter predominated in them. The existence of such objects could disprove the widely accepted cosmological model called the Lambda Cold Dark Matter (LCDM), according to which all galaxies should be surrounded by a dark matter halo. An article by researchers with a solution to the riddle was published in the Monthly Notices of the Royal Astronomical Society, briefly about the scientific work reported in a press release on Phys.org.
Scientists analyzed globular clusters in galaxies with stellar masses ranging from one hundred million to one hundred billion solar masses, generated in the Illustris cosmological simulation. From the dynamics of such clusters, one can determine the mass of dark matter in dwarf galaxies, where other indicators, such as smaller satellite galaxies, are absent. The simulated galaxies with properties of interest to astronomers were located in analogs of the Virgo galaxy cluster.
Researchers have discovered analogs of dwarf galaxies without dark matter, which contain about a billion stars (for comparison, there are 200-400 billion stars in the Milky Way). In the beginning, these galaxies had dark matter, but in the process of long evolution they lost 90 percent of invisible matter due to tidal forces from the cluster. This explains the origin of ultra-diffuse galaxies such as DF2 and DF4, which have extremely little dark matter.
Despite the fact that the nature of dark matter is still unknown, scientists do not doubt its existence, since they observe its direct effect on the dynamics of space objects. Invisible matter, which is an important part of the concept of the Universe, hardly interacts with photons, and this solves the problem of hidden mass, according to which there is a contradiction between the calculated and visible masses of objects.