Black holes in binary stellar systems and galactic nuclei
A.M. Cherepashchuk Lomonosov Moscow State University, Shternberg State Astronomical Institute, Universitetskii prosp. 13, Moscow, 119889, Russian Federation
In the last 40 years, after pioneering papers by Ya.B. Zeldovich and E.E. Salpeter in which a powerful energy release from nonspherical accretion of matter onto a black hole was predicted, a lot of observational studies of black holes in the Universe have been carried out. By the present time, masses of several dozens of stellar-mass black holes (MBH=(4 — 20) Mʘ) in X-ray binary systems and of several hundreds of supermassive black holes (MBH=(106 — 1010) Mʘ) in galactic nuclei have been measured. Estimated radii of these massive and compact objects do not exceed several gravitational radii. For about ten stellar-mass black holes and several dozens supermassive black holes, the values of the dimensionless angular momentum a* have been estimated, which, in agreement with theoretical predictions, do not exceed the limiting value a* = 0.998. A new field of astrophysics, the black hole demography, which studies the birth and growth of black holes, as well as their evolutionary connection to other objects in the Universe — stars, galaxies, etc., is rapidly developing. In addition to supermassive black holes, massive stellar clusters are observed in galactic nuclei, and their evolution is distinct from that of supermassive black holes. Evolutionary relations between supermassive black holes in galactic nuclei and spheroidal stellar components (bulges) of galaxies, as well as with dark matter galactic haloes emerge. The launch into orbit of the space radio interferometer Radioastron opened up the real possibility to finally prove that numerous massive and highly compact objects with properties very similar to those of black holes are real black holes in the sense of A. Einstein’s General Relativity. Similar proofs of the existence of black holes in the Universe can be obtained by intercontinental radio interferometry at short wavelengths $\lambda \lesssim 1$ mm (the international program “Event Horizon Telescope”).