Artist’s conception of star-forming gas erupting from Phoenix Cluster’s central galaxy  Image credit NASA/Chandra Observatory, Cambridge, Mass

The Phoenix Cluster is about 5,700,000,000 miles from Earth and is named as much for the constellation in which it is located as for its remarkable properties.

Michael McDonald, a Hubble Fellow at MIT and lead author of the paper published in Nature, explained, “While galaxies at the center of most clusters may have been dormant for billions years, the central galaxy in this cluster seems to have come back to life with a new burst of star formation.  The mythology of the Phoenix, a bird rising from the dead, is a great way to describe this revived object.”

The object is among the largest in the universe.

The supper-massive, super-bright, super-prolific cluster is birthing stars at a rate of more than 740 per year.

It’s more powerful than a steaming locomotive, in that it’s the most powerful producer of X-rays of any known cluster of galaxies.

McDonald said that Phoenix behaves so atypically that scientists were at first skeptical about what they were observing.  In most cases, jets of material from super-massive black holes at the centers of galaxies heat surrounding gases, which prevents them from reaching temperatures necessary for them to birth stars at high rates.

Brian McNamara, astrophysicist at Canada’s University of Waterloo and not  part of the study, said, ”For some reason this (heating) cycle isn’t working in the Phoenix Cluster, and we don’t know why—that’s the mystery.”

McDonald suggests that researchers have stumbled on a previously unknown, pivotal stage in the normal course of galactic evolution, a stage before its black hole becomes powerful enough to kick the heat into high gear.

“We suspect this phase should only last for about a 100,000,000 years,” he explained, “which is less than one percent of the age of the universe.  So it is not surprising that these systems are rare, since the odds of catching one during this starburst phase should be around one in a hundred.”

McNamara isn’t convinced, and said the Phoenix Cluster is “ . . . not behaving like most galaxies in cooling flows, and while we have lots of ideas for why this would be, we are not sure which, if any, are correct.”

Performance of the Phoenix Cluster is confirmed by NASA’s Chandra X-ray Observatory, the National Science Foundation’s South Pole Telescope, and eight other telescopes on Earth and in orbit.

Sources:  NASA, August 16, 2012    National Geographic, August 15, 2012   Study published in Nature, August 15, 2012




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