High-mass X-ray binaries

High-mass X-ray binaries (HMXB) are binary stars where one of the components is a neutron star or a black hole. The other component is a massive star, usually a Be star or a blue supergiant. A fraction of the stellar wind of the companion star is captured by the compact star, and produces X-rays as it falls onto the compact object.

In HMXB, the massive star dominates the emission of optical light. The compact object is the dominant source of X-rays. The massive stars are very luminous and therefore easily detected. One of the most famous HMXB is Cygnus X-1 which was the first stellar-mass black hole discovered.