|X-ray binary stars
A binary star system where one of the stars has evolved and collapsed into an extremely dense body such as a white dwarf, a neutron star, or a black hole. The enormous gravitational attraction of the massive, dense, but dim component pulls material from the brighter, less massive star in an accretion disk. The gravitational potential energy of the accreted matter is converted to heat by viscosity and eventually to high-energy photons in the X-ray range. The brightest X-ray binary is Scorpius X-1.