X-Ray Astronomy and Close Binary Systems.

The discovery in 1962 of the compact source Sco X-1, the first X-ray source located outside the Solar System, marked a new ("golden") era in the study of close binary systems (CBSs). Soon after, accreting neutron stars and first black hole candidates in CBSs were discovered. The ability to "weigh" neutron stars and black holes in CBSs made it possible to distinguish accreting black holes from neutron stars. The theory of accretion onto relativistic objects in CBSs has been developed, as well as the theory of the evolution of CBSs with mass exchange up to the latest stages, including binary black holes and neutron stars. CBSs have become the cutting edge of astrophysics. Subsequent observations of gravitation waves and observations with the EHT intercontinental radio interferometer with an angular resolution of ~10–5 arcsec made it possible to finally prove the existence of black holes in the Universe. Thus, the modern triumph of black holes has largely been due to the development of the science of CBSs. This paper is based on a presentation made in the astrophysical memorial seminar "Novelties in Understanding the Evolution of Binary Stars", dedicated to the 90th anniversary of Professor M.A. Svechnikov. [ABSTRACT FROM AUTHOR]