The animation above shows how large numbers of stars form in the Phoenix Cluster. It begins by showing several galaxies in the cluster and hot gas (in red). This hot gas contains more normal matter than all of the galaxies in the cluster combined, and can only be detected with X-ray telescopes like Chandra. The camera then flies in towards the large elliptical galaxy at the center of the cluster. The hot gas near this galaxy is giving off copious amounts of X-rays and cooling quickly over time, as shown by the change to a blue color. This cooling causes gas to flow inwards along filaments and form huge numbers of stars when it continues to cool. (NASA/CXC/A. Hobart)