Supermassive black holes sometimes merge, but for decades, astrophysicists have not known how. Now, we may finally have a solution in the form of dark matter.
After a pair of galaxies smash together, their central supermassive black holes usually begin to orbit one another. Over the course of many millions of years, these colossal black holes interact gravitationally with any nearby matter, flinging it away. This process generates friction that gradually slows down the black holes, pushing them to spiral closer and closer to one another.
