ABSTRACT
X-ray astronomy, i.e. studies of cosmic X-ray emissions and comparison of the results with data obtained using other astronomical techniques, opens up extremely wide opportunities for the investigation of hot cosmic plasma and relativistic cosmic electrons, which are of great importance for astronomy as a whole. X-ray astronomy studies the Sun, the stars, supernova shells, pulsars, quasars, galaxies, and the hot gas in galaxies and their clusters. The significance of the methods of X-ray astronomy cannot be overestimated. X-ray astronomy of "normal" stars is therefore becoming practicable, although until recently only special sources could be observed in the X-ray range, such as pulsars, X-ray pulsars, the neutron components of close binary systems and some other binary systems. The existence of high-power X-ray sources as components of close binary systems is quite understandable, since intense accretion occurs in such systems; that is, plasma flows from the lighter star to the heavier star.
