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V404 Cygni

V404 Cygni
The best case for a stellar black hole. Observations at X-ray and optical wavelengths have shown that this is a binary system in which a late G or early K star revolves, every 6.47 days, around 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.

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