A0620-00 (abbreviated from 1A 0620-00) is a binary star system in the constellation of Monoceros, with an apparent magnitude of 11.2.

[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.

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.

[6] On 15 June 2018, a signal was transmitted from the European Space Agency big radio antenna at Cebreros Station (77 kilometers west of Madrid, Spain), in memory of Stephen Hawking, who died on 14 March 2018, and his work on the physics of black holes.

The broadcast will travel the 3,457-light-year distance at the speed of light and will arrive in the year 5475; this will be the first-ever human interaction with a currently known black hole.