To have an extra-heavy black hole, a galaxy or bulge must, in addition to being massive, also be unusually small and dense. In other words, the mass of the hole is determined by whatever fixes the size of the bulge. The new correlation thus supports theories that quasars are black holes and bulges in the throes of growth. Such episodes, though not always so intense, may be a natural part of the life cycle of most galaxies, triggered by interactions or mergers with other galaxies. The quasar phase overlaps with the appearance of the first stars in the bulge.
Some galaxies then acquire a flattened disk, such as the one the sun lives in.
Other galaxies begin as a disk and later develop a bulge with a black hole. Richstone, however, worries that this scenario may contradict the available historical evidence, which suggests a gap in time between the onset of quasar activity and that of star formation. Kormendy disagrees but admits that the scenario is still sketchy. Nobody quite knows what created the seed hole that then grew to massive proportions, how material steered itself into the hole or why the beast decided to stop eating. The art of doing science is to try to get the right answer with imperfect data, he says.