Theorists have predicted that wandering black holes would roam the outskirts of galaxies as galaxies collide and merge. It means that we’re going to find many more examples of wandering black holes, and we can understand how galaxies and their black holes merge and build up over time.” The supermassive black hole that caused the event has about the same mass as the black hole at the center of our Milky Way Galaxy. If a third black hole from another merger enters the mix, complex three-body interactions would kick the smallest one out. “The key science question we want to answer is: How common are wandering black holes?”