The Perseus Cluster s X Ray Skull . ... NASA Explanation: This haunting image from the orbiting Chandra Observatory reveals the Perseus Cluster of Galaxies in x-rays , photons with a thousand or more times the energy of visible light. ... Instead of mere galaxies, a fifty million degree cloud of intracluster gas , itself more massive than all the cluster's galaxies combined, dominates the x-ray view . ... Like eyes in a skull, two dark bubbles flank a bright central source of x-ray emission. ...