24: Black Holes Feeding On Colliding Galaxies

There are a lot of galaxies in the universe — billions and billions of them, in fact. And many of them are in the process of collision: some collided long ago, some are merging right now, and some will slam together in the distant future. When they collide, the supermassive black holes in their cores can collide and merge too — and that's a pretty extreme event. Studying how fast these mergers take place is changing astronomers’ models of galaxy formation and evolution.