A supermassive black hole is the largest type of black hole in a galaxy, with a mass millions of times that of our sun .Though it can’t be imaged directly because black holes pull in all light, scientists have inferred its presence by looking at the speed and motion of stars and matter close to the galactic center. They have inferred that the movements are influenced by the gravitational pull of a black hole. No one knows how the black holes at the center of galaxies form, but some suspect that they may begin as a cluster of smaller black holes that merge, or as a smaller black hole that consumes enough matter to become a supermassive one.
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