Transcript: Careful studies from space have allowed us to make a census of the population of supermassive black holes in nearby galaxies. M31, our nearest neighbor and similar galaxy to the Milky Way, has a black hole about ten million solar masses. M87, the giant elliptical galaxy that dominates the Virgo cluster has a black hole that is much more massive, three times ten to the nine solar masses, three billion times more massive than the Sun. One survey found that twenty-five percent of all nearby galaxies have black holes, but the most important thing that’s been found out about black holes in nearby galaxies is that their mass is proportional to the bulge mass or luminosity. The bulge is the old stellar population that’s moving in elliptical orbits. Elliptical galaxies are essentially purely bulge population and are large, so they have the most massive black holes. Among spiral galaxies the black hole mass goes down according to the Hubble sequence. Higher black hole masses for Sa’s, lower for Sb’s, and lower still for Sc’s. The Milky Way fits this sequence with its black hole of a few million solar masses.