So how many supermassive black holes *are* there in Holmberg 15A anyway?

Around 760 million light years from Earth lies the galaxy cluster Abell 85, a mighty collection of about 500 galaxies all orbiting one another. At its center is the enormous elliptical galaxy Holmberg 15A… and I do mean enormous; some estimates put it at well over 50 trillion times the mass of the Sun, dozens of times more massive than the Milky Way.

All big galaxies have a supermassive black hole in their hearts, millions or billions of times the Sun's mass. In very rough terms the black hole ...