Cygnus X-1 is a well-known binary star system located in the constellation Cygnus. It consists of a massive black hole and a companion star, which is a blue supergiant. The black hole, formed from the collapse of a massive star, has a mass about 15 times that of the Sun. Discovered in the 1960s, Cygnus X-1 was one of the first strong black hole candidates identified. It emits X-rays as material from the companion star is pulled toward the black hole, creating an accretion disk that heats up and produces high-energy radiation.