V4641 Sagittarii

V4641 Sagittarii, V4641 Sgr short, is a microquasar in the constellation Sagittarius, which contains a black hole of about 10 solar masses.

History

This was discovered from a star and a compact component existing Duo September 15, 1999, after an X-ray outburst was observed. Calculations showed a mass of about 10 solar masses for the compact, not observable component. This value is well above the limit for a stable neutron star of about 5 solar masses. Therefore, only a black hole comes into question.

The distance of V4641 Sagittarii is not precisely known; earlier estimates of about 0.5 kpc, which would have made the object to the next known black hole, proved to be far too low.

The name follows the rules for naming variable stars and states that V4641 Sagittarii is the 4641st variable star, which was discovered in the constellation of Sagittarius.