High-mass X-ray binary

A high-mass X-ray binary (HMXB or HMXRB) is a binary star system containing a compact object (typically a black hole or neutron star) and a normal star more massive than approximately 8–10 solar masses (M_☉). They form when the more massive star in a binary undergoes a supernova explosion to become a neutron star or black hole, and then begins to accrete from the other star, which can be a supergiant, a Be star, or, rarely, a Wolf-Rayet star. The compact object, which is almost always a neutron star, usually accretes from the companion's strong stellar winds, releasing bright X-ray emission that can be observed by astronomers. This period ends when the companion begins to evolve and the binary either spirals in, forming a Thorne-Zytkow object, or becomes a binary system after the companion star explodes in a supernova.

There are several different types of HMXBs, all with different properties, modes of formation, and likely fates. Supergiant X-ray binaries, Be/X-ray binaries, and Wolf-Rayet X-ray binaries are systems containing a supergiant star, Be star, or Wolf-Rayet star respectively. X-ray pulsars contain strongly magnetized neutron stars that funnel accreted plasma onto their magnetic poles. Ultraluminous X-ray sources are HMXBs containing a compact object, likely a black hole, accreting faster than the Eddington limit. Finally, gamma-ray binaries are HMXBs that emit mostly in gamma-ray wavelengths due to interactions between their host pulsar's fast rotation and strong magnetic field. Recent launches of X-ray telescopes and studies of their data have allowed for the detection, identification, and analysis of many new HMXBs within every class.