Galaxies are made up of billions of stars, and they're constantly forming new stars from clouds of gas, mostly hydrogen.
Early galaxies had a lot of this gas, but they could have used it up too quickly, making tons of stars and then dying out.
But scientists now think that galaxies have a way to control their star formation, like a built-in regulator.
This regulator is a supermassive black hole at the center of the galaxy, which acts like a heart, pulsing and sending out energy that slows down the formation of new stars, making the galaxy last longer.
