Portal:Radiation astronomy/X-ray astronomy article/27

This X-ray image of Cygnus X-1 was taken by a balloon-borne telescope, the High Energy Replicated Optics (HERO) project. NASA image.

Cygnus X-1 (abbreviated Cyg X-1) is a well known galactic X-ray source in the constellation Cygnus. Cygnus X-1 was the first X-ray source widely accepted to be a black hole candidate and it remains among the most studied astronomical objects in its class. It is now estimated to have a mass about 8.7 times the mass of the Sun and has been shown to be too compact to be any known kind of normal star or other likely object besides a black hole.