A0620-00
A0620-00
Binary star in the constellation Monoceros
A0620-00 (abbreviated from 1A 0620-00) is a binary star system in the constellation of Monoceros, with an apparent magnitude of 11.2
A0620-00 consists of two objects. The first object is a K-type main-sequence star.[4][5] The second object cannot be seen, but based on its calculated mass of about 6 M☉,[8][4] it is too massive to be a neutron star and must therefore be a stellar-mass black hole.[7] The two objects orbit each other every 7.75 hours.[7] At a distance of roughly 3,300 light-years (1,000 parsecs) away, the black hole of A0620-00 would be one of the nearest known black holes to the Solar System, closer than GRO J1655-40.[10]
A0620-00 has undergone two X-ray outbreaks. The first one was in 1917.[11] The second burst, in 1975, was detected by the Ariel 5 satellite.[12] During that time, A0620-00 was the brightest X-ray point source.[7] It is now classified as an X-ray nova.[7] Its black hole nature was determined in 1986.[7]
The black hole in A0620-00 pulls matter from the K-type star into an accretion disk.[4] The accretion disk emits significant amounts of visible light and X-rays. Because the K-type star has been pulled into an ellipsoidal shape, the amount of surface area visible, and thus the apparent brightness, changes from the Earth's perspective. A0620-00 also bears the variable star designation V616 Monocerotis.[6]