The centers of as many as a tenth of all galaxies generate more energy than can be explained by stars, with some of these "active galactic nuclei" releasing more radiation than the entire Milky Way galaxy combined, but from a space no larger than our solar system. Astronomers suspect this energy is released when matter falls into giant, supermassive black holes that are up to billions of times the mass of our sun at these galaxies' cores.

"These monster black holes evolve in a way that is strongly related to the amount of dark matter that surrounds them and that is intimately related to the probability of galaxies to merge," said study lead author Nico Cappelluti, an astrophysicist at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany.[ MSNBC ]