|High mass x-ray binary stars
A member of one of the two main classes of X-ray binary systems where one of the components is a neutron star or a black hole and the other one a massive star. HMXBs emit relatively hard X-rays and usually show regular pulsations, no X-ray bursts, and often X-ray eclipses. Their X-ray luminosity is much larger than their optical luminosity. In our Galaxy HMXBs are found predominantly in the spiral arms and within the Galactic disk in young stellar populations less than 10^7 years old. One of the most famous HMXB is Cygnus X-1 which was the first stellar-mass black hole discovered.