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A Black Hole and Accretion Disk The above picture is of a black hole and its orbiting material. This orbiting material is referred to as an accretion disk. At the center of the milky way, and most other galaxies, is one very large version of a black hole. Called a supermassive black hole, it has an estimated mass in the millions of solar masses. This means that the mass of a few million stars like that of our own sun is equivalent to the mass of this behemoth. The accretion disk is our entire galaxy. Image credit:wallfox.net

Astronomers and Astrophysicists know that the center of our galaxy has a supermassive black hole because of long-term tracking of a few dozen stars in the galactic center using the Keck telescope. Each of the blue and yellow dots is a star. As the images show, the stars are quickly orbiting an object of very high mass. The mass has been measured, and found that only one thing can have this much mass in one small location: A supermassive black hole. Gif Credit: Keck/UCLA Galactic Center Group