What is the approximate mass of Sagittarius A* in solar masses?

The approximate mass of Sagittarius A* is 4.1 million solar masses.

Sagittarius A* is the supermassive black hole at the center of the Milky Way, about 26,000 light-years from Earth. Astronomers estimated its mass by tracking stars orbiting the Galactic Center, especially the star S2, whose rapid elliptical orbit reveals the strength of the central gravitational field. Applying Kepler’s laws shows that roughly four million Suns must fit inside a very compact region.

The value 4.1 million solar masses is an earlier widely cited estimate; more recent measurements place the mass near 4.3 million solar masses. That difference reflects improved observations and measurement methods, not a fundamentally different object. Sagittarius A* is therefore best described as approximately four million solar masses.

A common mix-up is confusing the black hole’s mass with the mass of the entire central region of the Milky Way. The surrounding stars, gas and dark matter contribute additional mass, but Sagittarius A* itself accounts for the extraordinarily dense central object. In 2022, the Event Horizon Telescope also produced the first image of its glowing surroundings.