By now, merging black holes and the gravitational waves they produce are a scientific surety. Astronomers have observed several black hole mergers, all between stellar-mass black holes less than 100 times the mass of our sun. But no mergers between supermassive black holes, those with masses millions or billions times that of our star, have ever been seen; and in fact, astronomers wonder how likely such a smash-up would be. Now, the discovery of two supermassive black holes headed right for each other could help scientists answer the question of what would happen if they were to meet.
This particular pair, each more massive than 800 million suns, lies in a galaxy 2.5 billion light-years away. The galaxy itself is a merger remnant — all that’s left after two galaxies, each hosting a supermassive black hole, combined. A team led by Andy Goulding at Princeton University made the find using the Hubble Space Telescope and published their discovery July 10 in The Astrophysical Journal Letters.
