Tags: Star.
V4641 Sagittarii (V4641 Sgr) is a variable X-ray binary star system in the constellation Sagittarius. It is the source of one of the fastest superluminal jets in our galaxy.In 1999 a violent X-ray outburst revealed it to contain a black hole. At the time it was considered to be the closest known black hole to Earth at a distance of approximately 1600 light-years (490 pc). Later observations showed it to be at least 15 times farther away.