Most of the ordinary matter in the universe is hydrogen. But surprisingly, less than 20% of this hydrogen sits inside galaxies. The rest lies in the vast spaces between them – the so-called intergalactic medium. >This cosmic reservoir is thought to fuel the birth of new stars, as gas slowly falls into galaxies over billions of years. Yet much of that material doesn’t stay put: supernova explosions and powerful outflows from supermassive black holes can fling gas back out into intergalactic space. >The push-and-pull between inflows and outflows is central to understanding how galaxies grow and change over cosmic time…