Figure 26-20: “Bottom-Up” Galaxy Formation: Simulation This image is taken from a cold dark matter simulation like that shown in Figure 26-15. A portion of the universe is shown at a time 2.2 billion years after the Big Bang, corresponding to redshift z = 3.04. The colors indicate the density of gas: Yellow is highest, red is medium, and blue is the lowest density. Over time, the gas tends to pile up at points where filaments intersect, forming galaxies and clusters of galaxies.
(T. Theuns, MPA Garching/ESO)