What kind of object is Sagittarius A*?

Sagittarius A* is a supermassive black hole at the center of the Milky Way. It lies in the Galactic Center, roughly 26,000 light-years from Earth, and has a mass of about 4.3 million Suns.

The object was first identified as a compact radio source in 1974; the asterisk was added in 1982 to indicate an especially exciting radio source. Astronomers established its nature by tracking stars orbiting an enormous mass packed into a very small region, especially the star S2.

A common mix-up is confusing Sagittarius A* with Sagittarius A, the larger radio-source complex that includes the black hole, surrounding gas, and other structures. The black hole itself cannot be seen directly because light cannot escape its event horizon. In 2022, the Event Horizon Telescope released the first image of its glowing surroundings, showing the shadow-like central region against hot gas.