X-ray binary Cygnus X-1. Computer artwork of the high-mass X-ray binary called Cygnus X-1. It consists of a blue supergiant star (right) called HDE 226868, orbiting what is probably a black hole. The black hole is sucking gas from the blue star's atmosphere, leading to the formation of an accretion disc around the black hole (lower left). A black hole is a region of space in which the gravitational field is so strong that even light cannot escape. They are thought to form in supernovae, the explosive deaths of massive stars. Cygnus X-1 is around 82,000 light years away, in the constellation of Cygnus.