V404 Cygni

V404 Cygni is a binary star system in which there is a black hole. Observations at X-ray and optical wavelengths have shown the system contains a late G or early K star that orbits, every 6.47 days, a compact companion with a probable mass of 8 to 15 solar masses, well above the mass limit at which a collapsed star must become a black hole. Most of the time the X-ray emission is quiescent, indicating only a slow trickle of material from the bright star onto the black hole's accretion disk.


V404 Cygni


In 2009, the distance to V404 Cygni was determined accurately by stellar parallax to be 7,800 ± 460 light-years (2,390 ± 140 pc).