Annotation of the results obtained in 2023
The evolution of a binary system consisting of two clusters of primordial black holes has been studied. Such systems could have formed at an early radiation-dominated stage of the Universe evolution, and mergers of central massive black holes in these clusters may explain some of the gravitational wave signals recorded by LIGO-Virgo-KAGRA detectors. It is shown that clusters influence each other with tidal forces, resulting in tidal dissipation transforming the energy of the orbital motion of the two clusters into their internal energy. Differential equations describing the evolution of the orbit of two clusters of primordial black holes were obtained and solved, taking into account tidal dissipation and energy losses due to the radiation of gravitational waves. It was shown that at an early stage of the orbital evolution of two clusters, tidal forces lead to rapid circularization of the binary system and only after that energy losses in the form of gravitational waves begin to prevail, as a result of which the clusters eventually merge. Since clusters in the model under consideration contain a massive central primordial black hole, their central black holes will merge when clusters merge. The corresponding rate of mergers of massive primordial black holes was calculated and it was shown that it is compatible with the data of LIGO-Virgo-KAGRA collaboration even in the case when all dark matter consists of primordial black holes. The results of this work are published in the article [Yu. Eroshenko, V. Stasenko, Symmetry 15, 637 (2023)]. The detection of correlated movements of trans-Neptunian objects has led to the hypothesis that the 9th planet or primordial black hole with a mass of 5-15 Earth masses may be located at a distance of 300-1000 astronomical units from the Sun. An important task is to search for possible observational manifestations of the 9th planet or black hole, on the basis of which this hypothesis could be tested. Within this work, it is shown that if there is a similar massive object on the periphery of the Solar System, then with its gravitational field it perturbs the orbits of dust particles, and some of the particles can fall into the inner region of the Solar System, flying inside the Earth's orbit. The dust flow turned out to be comparable in magnitude to what is actually observed by counting dust particles on the ice of Antarctica and by direct measurements on spacecraft. This suggests that some of the observed dust flow may come to Earth from the Oort Cloud under the influence of the gravitational field of the 9th planet or the primordial black hole. The problem of the probability of capturing such an object into the Solar system is also investigated. If planets could be captured from the disk of the Galaxy and from the protostellar cloud at the stage of the Sun formation, then the primordial black holes could be captured only from the halo. The corresponding calculations were performed, which showed that the probability of capture from the halo is very low. The results obtained are published in the works of [Yu. N. Eroshenko, E. A. Popova, Astronomicheskii Zhurnal, 100, 1056 (2023)] and [Yu. N. Eroshenko, New Astronomy 103, 102057 (2023)]. In recent years, a number of theoretical studies have found that density spikes of dark matter can occur around primordial black holes at the stage of radiation dominance if dark matter consists of a new type of elementary particles. The annihilation of dark matter in such spikes, especially in their central region, is very important for the search for observational manifestations of primordial black holes and dark matter. In this project, preliminary calculations of the formation of a density spike around a primordial black hole have been performed, taking into account the annihilation of dark matter particles, and analytical expressions have been written for further complete numerical solution of the problem. Unlike previous studies, the formation of a density spike and annihilation are considered simultaneously, since particle losses during annihilation significantly affect the profile in its central region. This task required consideration of a single metric having as asymptotics the Schwarzschild metric and the Friedman metric at small and large distances, respectively. Modern theoretical models admit the existence of supermassive primordial black hole in the universe. To test these theories, radio telescopes can be used to search for absorption in a 21 cm line in baryon halos around such black holes at the stage before the reionization of the universe. To do this, it is necessary to find out in detail the structure of the baryon halo and the degree of ionization of gas in it at various distances from the black hole. Previously, these calculations were carried out mainly at the level of estimates by order of magnitude. Within the framework of this project, a more accurate quantitative study is being conducted. To date, a system of equations has been written down to calculate the evolution of the baryon halo around supermassive primordial black holes in the pre-galactic epoch, taking into account the interaction with radiation from the accretion of matter onto the black hole. This radiation creates a force of radiation pressure and causes partial ionization of the gas. A numerical algorithm has been developed and is being debugged for the subsequent numerical solution of the problem.

 

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