A supermassive black hole is the largest type of black hole, with mass on the order of millions to billions of times the mass of the Sun. Most, if not all, galaxies are thought to contain a supermassive black hole at their centers, including Sagittarius A* at the center of the Milky Way.
efficiency. The Milky Way is a barred spiral galaxy containing 100–400 billion stars. At its center lies Sagittarius A*, a supermassive black hole around which the entire galaxy rotates.