X-ray binary

An X-ray binary (XRB) or binary X-ray system is a binary star that produces X-rays. They are ascribed to the inclusion of a neutron star or stellar-mass black hole that is accreting from its companion, producing X-rays through shock. They are often classified by the mass of the compact object's companion:

• low-mass X-ray binaries (LMXB)
• intermediate-mass X-ray binaries (IMXB)
• high-mass X-ray binaries (HMXB or massive X-ray binaries, MXRB)

With a strong magnetic field, the binary might produce periodic X-ray pulses, i.e., an X-ray pulsar. Otherwise, it may produce occasional burst-transients, (X-ray bursts), i.e., an X-ray nova aka X-ray burster. The bursts may be due to varying levels of accretion. A Be X-ray binary (BeXRB) is a such a binary that includes a Be star.

X-ray binaries are one of the methods of detecting stellar-mass black holes: over a hundred Milky Way X-ray binaries suggests a black-hole companion.