The new theory of self-interacting dark matter allowed scientists to explain why in two distant galaxies from the constellation of China there is less than it should be. The results of the study have been published in the journal Physical Review Letters.
It is believed that most of the substance in the Universe is represented by dark matter. Its nature is not quite clear. Unlike ordinary matter, it does not absorb, reflect, or emit light, and can only be detected by indirect signs such as gravitational interaction.
Today, the theory of cold dark matter (CDM – Cold dark matter) prevails among scientists, according to which particles of dark matter do not collide with each other or with particles of ordinary matter.
The newer theory of self-interacting dark matter (SIDM – Self-interacting dark matter) suggests that particles of dark matter interact with each other by means of the so-called dark force.
Both theories explain how the general structure of the universe appears, but they describe the distribution of dark matter in the inner regions of galaxies in different ways. Scientists from the USA and China have compared how both theories work with a concrete example of two galaxies from the constellation of China.
Galaxies NGC 1052-DF2 and NGC 1052-DF4, satellites of the larger NGC 1052, are located about 65 million light-years away from us and belong to the ultra-diffuse class because their luminosity is very low. It was assumed that with a small number of stars, the share of dark matter in such galaxies is particularly high, but observations showed the opposite.
The researchers assumed that these galaxies lost most of their dark matter due to the gravitational influence of the massive neighbor NGC 1052. To test their idea, they carried out a computer simulation of this process, based on the positions of both CDM- and SIDM-models.
“It is believed that dark matter dominates the total mass of the galaxy,” the words of Associate Professor of Physics and Astronomy Hai-Bo Yu, who directed the study, are quoted in a press release from the University of California at Riverside. – Observations of NGC 1052-DF2 and NGC 1052-DF4 show, however, that the ratio of dark matter to their stellar masses is about one, which is 300 times lower than expected. To eliminate the discrepancy, we calculated that the DF2 and DF4 halos may lose most of their mass due to tidal interactions with the massive galaxy NGC 1052″.
It turned out that the new theory explains the loss of dark matter by DF2 and DF4 galaxies much better than the traditional one. In the CDM model, the inner halo of dark matter must be too stiff and resistant to tidal forces from the neighboring massive galaxy, while the scientists observe quite differently. The SIDM model, on the contrary, shows that dark matter particles in this scenario are pushed out of the inner regions of galaxies into the outer regions, blurring the strength of the halo.
The idea of invisible dark matter was expressed back in the 1930s when astrophysicists noticed that distant galaxies moved much faster than their visible mass should allow.