Galaxy cluster is a star-forming powerhouse

Posted at 10:15 PM, Aug 15, 2012
and last updated 2012-08-15 20:12:16-04

(CNN) — The Olympics may be over, but in outer space, records are still being broken.

Scientist announced Wednesday the discovery of the Phoenix cluster, one of the most massive and luminous galaxy clusters ever identified. It’s about 5.7 billion light years away, so we are getting a sense of it as it was at that time, billions of years ago.

The cluster has a mass of 2,500 trillion times that of our sun, said Michael McDonald, researcher at Massachusetts Institute of Technology, in a news conference Wednesday. It contains hundreds of thousands of galaxies the size of the Milky Way, in addition to dark matter and hot gas.

In a race to form new stars, this cluster leaves our Milky Way in the dust.

Impressively, the central galaxy in the cluster produces about 740 new stars per year, a rate that is unmatched by any other known galaxy at the center of a cluster. By comparison, the Milky Way forms about one to two new stars each year.

The Phoenix cluster also breaks the record for being the brightest cluster in the X-ray radiation spectrum. The gas in the cluster is about 100 million degrees Kelvin; our sun is cooler, by comparison.

Scientists used the Chandra X-Ray Observatory, a space telescope, to investigate clusters that the South Pole Telescope had helped to identify as interesting. The Phoenix cluster appeared unique.

Astrophysicists are still trying to understand how galaxies got their stars. Gas needs to cool down and become dense in order to form stars, but that process is still an open research question, said Megan Donahue, professor of astronomy at Michigan State University in East Lansing. Only about 10% of the gas in universe is in stars.

In other clusters, such as Perseus, a black hole doesn’t allow gas to cool and form stars so quickly. That’s because the black hole releases powerful jets, which push gas out of the way, said Martin Rees, professor of cosmology and astrophysics at the University of Cambridge, United Kingdom, who was not involved in the research. The jets produce sound waves that release energy and help prevent the formation of stars, since the gas can’t cool.

That’s not the case with the Phoenix cluster. There’s probably a fairly massive black hole in the central galaxy of the Phoenix cluster, but it’s not putting out the same energy seen in other clusters, said Martin Rees, professor of cosmology and astrophysics, University of Cambridge, United Kingdom, who was not involved in the research.

“The infall rate of the gas is at this exceptional rate, because there’s so much hot gas in this cluster, it’s a very big dense cluster,” he said. “This gas is raining down, and it just can’t compete.

So the “tussle” between black holes and gas is won by the gas in the Phoenix Cluster, Rees said, but not in the Perseus Cluster.

“It’s by studying these extreme objects, and hoping to find more of them, that we really understand the symbiosis between galaxies and their black holes,” Rees said.

If scientists could observe the cluster now, rather than as it was billions of years ago, it would be an “exceptionally bright galaxy” with a black hole with a mass of 10 billion suns, Rees said. It would not be quite as blue; blue light indicates younger stars, while red light is the signature of older stars.