Cygnus X-1 is a galactic X-ray source in the constellation Cygnus.
Cygnus X-1 is a massive galactic x-ray source located in the constellation Cygnus (Swan), only 6,000 lightyears away. A black hole with ~20 times the mass of the Sun was found to cause the strong radiation. Its event horizon is about 300 km. It was the first black hole to be observed. The black hole forms a binary system with a massive star and is orbiting this 20-40 solar mass blue supergiant every 5.6 days. Cygnus X-1 continuously accretes (sheds) matter that spirals onto its event horizon from its blue supergiant companion.
X-ray image of the bright source Cygnus X-1 taken by a balloon-borne telescope, the High-Energy Replicated Optics (HERO) project.
Artist's impression of the Cygnus X-1 binary system. The black hole accretes matter that spirals onto its event horizon from its blue supergiant companion. Credit: ESA/Hubble illustration.