Chandra has mapped thousands of supermassive black holes using x-ray emissions. These correspond to the enormous emissions generated at the center of these galaxies, and not the run-of-the-mill singularities within the Milky Way that we all know to represent a grave threat to America's nebulae. The red-blue scale coloration of the dots represents low-to-high energy x-rays emitted, and therefore the mass of the black holes. It isn't as though their locations are somehow mysterious since these are all at galactic centers. It has certainly inspired me see what the relationship between BH mass and the type of galaxy. I am fairly sure that spirals have bigger AGN, but not completely.