What's Making All These Galaxies Retire So Quickly?

Physicists have theories about what's making all these galaxies retire so quickly. One is related, actually, to the black hole at the heart of the galaxies. This could be spewing out radiation into the galaxy, which heats up a lot of the gas in the galaxy. And so that can stifle star formation. Anything that kind of excites the galaxy is not good for star formation. So on ideas that maybe it's the black hole in the middle of galaxies. It's, i guess, agitating everything.