Pairs of supermassive black holes in the hearts of two quasars appear to be whirling around each other like cosmic eggbeaters. Eventually, they may merge to form even bigger black holes. A quasar is a supermassive black hole that’s pulled in vast amounts amounts of material from its parent galaxy, surrounding itself with a disk of superhot gas. The disk shines as brilliantly as billions of stars, so it’s visible across vast distances. The light from most quasars flickers randomly as the black hole ingests varying amounts of material. But recently, astronomers have seen a couple of quasars that vary in a pattern that repeats over a period of months or years. The astronomers suggest that these quasars contain two black holes that are in close orbit around each other — as little as a few hundred billion miles. As the black holes circle each other, we see the individual disks around them from different angles, so we see first one disk, then the other. As a result, the light from these syst
