Discovery: Bruce Balick and Robert L. Brown discovered Sagittarius A* in 1974. Brown added the asterisk in 1982 to distinguish the compact radio source from the larger Sagittarius A region.  Location: Sagittarius A* is located near the border of the constellations Sagittarius and Scorpius, about 5.6° south of the ecliptic.  Mass: Sagittarius A* has an estimated mass millions of times that of the Sun.   Radio waves: Sagittarius A* is a strong source of radio waves.  Event horizon: The event horizon of the black hole has a radius of 12 million km (7 million miles).  Observations: In 2015, NASA observed an X-ray flare from Sagittarius A* that was 400 times brighter than usual.  Image: In May 2022, the Event Horizon Telescope released the first image ever taken of Sagittarius A*.
