Alexander Knebe

The night sky seems full of stars, but between them lurk clouds of gas where not a single star has ever ignited. Such objects are called dark galaxies: they contain enough gas, but it is too diffuse and cold to collapse into stars.

Galaxy NGC 4254 lies 1.5 million light-years from the center of the Virgo cluster. It drags a long stream of cooling hydrogen — a sign that it's plowing headlong into the hot gas. Losing cold fuel quenches the birth of new stars.