https://www.vice.com/en_us/article/9kepy8/watch-this-ultra-hypnotic-supercomputer-simulation-of-galaxies-feasting

Galaxies are ravenous eaters. In addition to occasionally cannibalizing each other, galaxies are constantly feeding on gases strewn across the vast spaces that separate them.

These gases spill into the intergalactic medium when stars explode into supernovae, and are subsequently recycled when they are sucked back into galaxies to fuel the formation of new stars.