A Note on the Perseus Cluster . ... CXC , NASA Explanation: A truly enormous collection of thousands of galaxies, the Perseus Cluster - like other large galaxy clusters - is filled with hot, x-ray emitting gas. ... In other words, sound waves , likely generated by bursts of activity from the black hole, are ringing through the Perseus Galaxy Cluster. Astronomers infer that these previously unknown sound waves are a source of energy which keeps the cluster gas so hot. ... NASA Official: Jay Norris. ...