The Evolutionary Status of the Galaxy’s X-ray Binary Stars

Abstract

The article is devoted to the analysis of the evolutionary status of the X-ray binary stars of the Galaxy. It is shown that the assumption of the conservative evolution of these binary systems leads to an overestimation of the X-ray luminosity of the Galaxy by 3–4 orders. The total observed rate of accretion of matter by relativistic components of X-ray binaries is close to \( {\sim} {{10}^{{ - 6}}}{{M}_{ \odot }}{\text{/}}\)yr, while the theoretically possible rate reaches \( {\sim} {{10}^{{ - 2}}}{{M}_{ \odot }}{\text{/}}\)yr. The contradiction between these estimates is eliminated if two factors are taken into account. The first of them is the formation of a common envelope in massive X-ray binary systems after filling the Roche lobe by the donor and the brief phase of a bright X-ray source. The common envelope eliminates the output of X-ray radiation generated during accretion, and also leads to the loss of part of the donor’s matter from the system. The second factor is the presence of intense stellar wind of donors in massive X-ray binary, as well as the occurrence of induced stellar wind in low-mass donors due to exposure to hard radiation from an accreting relativistic star. At the same time, the generally accepted assumption that donors of X-ray binaries fill their Roche lobes may not be fulfilled. A significant part of the donor’s wind matter may be lost from the system. In addition, radiation can enhance the stellar wind of the accretion disk, and part of this wind will also leave the system. There are other factors that reduce the total number of accreted matter: supernova explosions in X-ray binaries, destroying part of these systems, the impossibility of accretion onto rapidly rotating young neutron stars with a strong magnetic field, as well as a rapid drop in the rate of loss of matter by the donor as its mass decreases, characteristic for low-mass X-ray systems.