Astronomers have found a galaxy cluster that is one of the largest objects in the known universe, and it is breaking records. The cluster, named the Phoenix cluster, has been observed by NASA's Chandra X-ray Observatory, the National Science Foundation's South Pole Telescope, and eight other observatories. Their findings suggest that the evolution of galaxy clusters may be more complicated than previously thought.
The most perplexing observations for astronomers are the facts that the rate of star formation and hot gas cooling in the middle of the Phoenix cluster are the highest ever observed. It is also the most powerful X-ray-producing cluster ever discovered. These observations were outlined in a study published this week in the journal Nature.
"While galaxies at the center of most clusters may have been dormant for billions of years, the central galaxy in this cluster seems to have come back to life with a new burst of star formation," said Michael McDonald, a Hubble Fellow at the Massachusetts Institute of Technology and the lead author of the study. "The mythology of the Phoenix, a bird rising from the dead, is a great way to describe this revived object."
Galaxy clusters are thought by astronomers to be prevented from Phoenix-type growth by a supermassive black hole located in the central galaxy of a cluster. Those black holes release jets of energy into the cluster and prevent the hot gas in the system from cooling, condensing, and forming new stars. The energy being released by the black hole in the Phoenix cluster is not powerful enough to prevent the cluster's gas from cooling, and so stars in the cluster are forming at around 20 times faster than in the Perseus cluster - a relatively normal galaxy cluster. As a result, astronomers predict that its rapid growth end relatively soon.
"The galaxy and its black hole are undergoing unsustainable growth," said study co-author Bradford Benson, of the University of Chicago. "This growth spurt can't last longer than about a hundred million years. Otherwise, the galaxy and black hole would become much bigger than their counterparts in the nearby universe."
(Photos courtesy NASA/CXC/MIT/JPL-Caltech/AURA/NOAO/CTIO/M.McDonald [left] and NASA/CXC/M.Weiss [right])