How do astronomers discover supermassive black holes in galaxy centers?
Quick Answer
They track stars and gas orbiting an invisible compact object, sometimes at speeds of thousands of kilometers per second. The Milky Way’s central black hole, Sagittarius A*, was confirmed this way.
The Full Story
Astronomers infer supermassive black holes by measuring the motion of nearby stars and gas. If those objects orbit something extremely massive but compact and invisible, the best explanation is a black hole. In our own galaxy, decades of observations by teams led by Andrea Ghez and Reinhard Genzel tracked stars near Sagittarius A*. More recently, the Event Horizon Telescope produced the first image of a black hole shadow in M87 in 2019 and of Sagittarius A* in 2022. These observations confirmed that supermassive black holes are common in galaxy centers.
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