Edmund Christian Herenz

A galaxy is more than just a stellar island. Surrounding it, far beyond the edge of the visible disk, hangs a tenuous cloud of gas. It barely emits light, but it is through this cloud that the galaxy breathes: drawing in fresh hydrogen to form new stars and expelling processed material after supernova explosions.

After the Big Bang, the Universe was filled with cold gas — mostly neutral hydrogen and helium. It enveloped the cosmos like a morning fog, impenetrable to light. The Dark Ages began. When the first galaxies ignited, their radiation, like a searchlight beam, started knocking electrons out of atoms.