Supermassive Black Holes on a Collision Course?
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.