Excellent summation and examples. Technically, to summarize even farther for OP, I would say that the supermassive black holes at the center of galaxies are the accretions of the matter that coalesced into a galaxy. Edit: I suppose you could say that the galaxy is an “accretion disk” in the making. Edit: Which begs the question; Do stars inevitably spiral into the supermassive black hole in the center of the galaxy or does the gravity from all of the stars, orbiting the center of the galaxy, balance everything out? I’m assuming the latter, however, off to research!