There's one thing that could unseat a supermassive black hole in this manner, the researchers say: gravitational waves. This suggested that galaxy 3C 186 had recently merged with another system, and perhaps their black holes merged too. An artist's conception of how gravitational waves could propel a black hole from the center of a galaxy. If the black holes had unequal masses and spin rates, they might have sent more gravitational waves in one direction than the other. When the collision was complete, the newly merged black hole would have then recoiled from the strongest gravitational waves, shooting off in the opposite direction.

Source: Washington Post March 24, 2017 18:14 UTC