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A0620-00 (abbreviated from 1A 0620-00) is a binary star system in the constellation of Monoceros.
A0620-00 consists of two objects. The first object is a K-type main-sequence star with a spectral type of K5 V. The second object cannot be seen, but based on its calculated mass of 6.6 M☉, it is too massive to be a neutron star and must therefore be a stellar-mass black hole. At a distance of about roughly 3,300 light-years (1,000 parsecs) away, this would make A0620-00 one of the nearest known black holes to the Solar System, closer than GRO J1655-40. The two objects orbit each other every 7.75 hours.A0620-00 has undergone two X-ray outbreaks. The first one was in 1917. The second time, in 1975, the burst was detected by the Ariel 5 satellite. During that time, A0620-00 was the brightest X-ray point source. It is now classified as an X-ray nova. Its black hole nature was determined in 1986.

The black hole in A0620-00 pulls matter from the K-type star into an accretion disk. 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.

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