An X-ray emitting binary system consisting of a neutron star (or in a few cases a black hole) and a normal stellar companion. They are divided into two groups according to the mass of the companion. In a low-mass X-ray binary (LMXB), for example Scorpius X-1, the normal star is less than about 2 solar masses; it is greater than about 10 solar masses in a high-mass X-ray binary (HMXB), such as Cygnus X-1. Binaries with intermediate-mass companions are very rare. The X-ray emission is a result of accretion of material from the companion on to the neutron star.
Subjects: Astronomy and Astrophysics.