LIGO Has Seen Several Intermediate Mass Black Hole Mergers

There are three known types of black holes: supermassive black holes that lurk in the hearts of galaxies, stellar mass black holes formed from stars that die as supernovae, and intermediate mass black holes with masses between the two extremes. It's generally thought that the intermediate ones form from the mergers of stellar mass black holes. If that is true, there should be a forbidden range between stellar and intermediate masses. A range where the mass is too large to have formed from a star but too small to be the sum of mergers. But a new study of data from LIGO suggests that there are black holes in that forbidden range.