An Etymological Dictionary of Astronomy and Astrophysics

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.

See also: → X-ray; → binary.