Object Analysis

Cygnus X-1 is a galactic X-ray source in the constellation Cygnus and was the first such source widely accepted to be a black hole. It was discovered in 1964 during a rocket flight and is one of the strongest X-ray sources seen from Earth. The system is located about 6,000 light-years away.

The system is a high-mass X-ray binary, consisting of a blue supergiant variable star (HDE 226868) and the compact black hole. The two orbit each other every 5.6 days. The stellar wind from the supergiant is captured by the black hole's gravity, forming an accretion disk that heats up to millions of degrees, generating the intense X-rays observed by astronomers.

Cygnus X-1 was the subject of a famous friendly bet between physicists Stephen Hawking and Kip Thorne in 1974. Hawking bet that it was not a black hole (as a form of insurance policy on his life's work), but he conceded the bet in 1990 as observational evidence mounted. The object is estimated to have a mass of about 21 times the mass of the Sun.