M sun black hole in our own Galactic Center. Key Results Supermassive black holes are relatively common and found in nearly every nearby bright galaxy. The numbers of black holes being found is consistent with what is expected from the number of quasars in the distant past. The mass of the black hole is proportional to the mass of the host galaxy. Today there are very few bright quasars in the nearby universe.
Larger galaxies have larger central black holes.
The correlation is very tight. Larger galaxies need more pieces to merge together to build them up. The more seeds, the larger the mass of the subsequent central black hole. As the stars in the galaxies evolve, they shed mass by winds. The evidence all points towards the existence of supermassive black holes in the centers of bright galaxies.