In the early cosmos, billions of years ago, galaxies resided in the equivalent of urban or country environments. Those that dwelled in crowded areas called clusters also experienced a kind of opulence, with lots of cold gas, or fuel, for making stars. Today, however, these galactic metropolises are ghost towns, populated by galaxies that can no longer form stars. How did they get this way and when did the fall of galactic cities occur? Read more on The Daily Galaxy.