Cygnus X-1

Cygnus X-1 (abbreviated Cyg X-1) is a well-known Milky Way galaxy X-ray source and black hole. It is one of the strongest X-ray sources seen from Terra. Cygnus X-1 is about five million years old and formed from a progenitor star that had more than 40 solar masses. It is now estimated to have a mass of about 14.8 solar masses. The radius of its event horizon is about 44 km.