A Tour of Perseus and Virgo Clusters

Narrator (April Hobart, CXC): Galaxy clusters are enormous. In fact, they are the largest objects in the Universe held together by gravity. Just one galaxy cluster can contain hundreds or even thousands of individual galaxies. And what may be more interesting is that these galaxies make up just a fraction of the mass in these clusters. In addition to dark matter, the bulk of the mass in clusters actually comes from vast amounts of very thin gas. This gas is so hot that it only reveals itself in X-ray light. For many years, scientists have wondered why the hot gas doesn’t cool and form lots of stars. With Chandra, astronomers have looked at many galaxy clusters, and in some, they found giant cavities carved out of the hot gas. They realized that the supermassive black holes at the centers of these clusters were pumping energy out into the gas through powerful jets. Now researchers have direct evidence for just how that energy keeps the gas in the entire galaxy cluster so hot. The answer may be turbulence. The same phenomenon that causes a bumpy airplane ride also prevents the hot gas in these galaxy clusters from ever settling down enough to cool. So while there are still many new things to learn about galaxy clusters, scientists may be finally homing in on the answer to one question that they have been asking for decades.