What class of object is Sagittarius A*?

Sagittarius A* is a supermassive black hole at the center of the Milky Way.

Usually abbreviated Sgr A*, it lies in the direction of the constellation Sagittarius and is the compact object marking the Galaxy’s dynamical center. Although the black hole itself emits no visible light, astronomers infer its presence from the rapid orbits of nearby stars and from radiation produced by hot gas around it.

The star S2 is especially important: it follows a tight, fast orbit around the Galactic Center, allowing researchers to estimate that the central object contains about 4 million times the Sun’s mass. That mass is compressed into a very small region, ruling out ordinary star clusters and supporting the black-hole interpretation.

In 2022, the Event Horizon Telescope released the first image of the glowing material surrounding Sgr A*. The image shows the black hole’s shadow against hot gas; it is not a conventional photograph of the black hole itself. Sagittarius A* is therefore not a neutron star, white dwarf, or star cluster.