V4641 Sagittarii

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 the Milky Way 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 1,600 light-years (490 pc). Later observations showed it to be at least 15 times farther away.