Cygnus X-1

Etymology
. From being the first discovered discrete astronomical X-ray source (an X-ray star) located in the constellation of Cygnus.

Proper noun

 * 1) A placename.
 * 2)  The first generally accepted and confirmed black hole. A black hole in a high-mass X-ray binary (HMXB) with a blue supergiant companion (HD 226868), located in the constellation Cygnus.
 * 3)  The high-mass X-ray binary star system containing this black hole and blue supergiant star.

Synonyms

 * abbreviation