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Galaxy cluster 'bustling' with star births detected
Posted On: Aug 16, 2012
The hot gas in Phoenix is giving off copious amounts of X-rays and cooling quickly over time, especially near the centre of the cluster, causing gas to flow inwards and form huge numbers of stars. These features are shown in this artist's impression of the central galaxy, with hot gas shown in red, cooler gas shown in blue, the gas flows shown by the ribbon-like features and the newly formed stars in blue. A NASA photo
A huge galaxy cluster - one of the largest objects in the Universe - producing stars at a very high rate has caught the attention of astronomers.
Observations made by world's 10 different telescopes, including NASA's Chandra X-ray Observatory, have found that the Phoenix galaxy cluster, located about 5.7 billion light years from Earth, is producing huge numbers of stars.
Stars are forming in the Phoenix cluster at the highest rate ever observed for the middle of a galaxy cluster.
The celestial object also is the most powerful producer of X-rays of any known cluster and among the most massive. The data also suggest the rate of hot gas cooling in the central regions of the Phoenix cluster is the largest ever observed.
"While galaxies at the centre 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," according to Michael McDonald, a Hubble Fellow at the Massachusetts Institute of Technology and lead author of a paper appearing in the Aug. 16 issue of the journal
"The mythology of the Phoenix, a bird rising from the dead, is a great way to describe this revived object," says the researcher.
The Phoenix cluster, like other galaxy clusters, contains a vast reservoir of hot gas, which itself holds more normal matter - not dark matter - than all of the galaxies in the cluster combined. As per theory, this hot gas should cool over time and sink to the galaxy at the centre of the cluster, forming huge numbers of stars.
However, most galaxy clusters have formed very few stars during the last few billion years. Astronomers think the supermassive black hole in the central galaxy of a cluster pumps energy into the system, thereby preventing cooling of gas from causing a burst of star formation.
The famous Perseus cluster is an example of a black hole bellowing out energy and preventing the gas from cooling to form stars at a high rate.
However, in the Phoenix cluster, the supermassive black hole at its core is producing jets not powerful enough to interfere in star formation. "The Phoenix cluster is showing us this is not the case...Jets from the giant black hole at the centre of a cluster are apparently not powerful enough to prevent the cluster gas from cooling," said co-author Ryan Foley, a Clay Fellow at the Harvard-Smithsonian Center for Astrophysics in Cambridge.
With its black hole not producing powerful enough jets, the centre of the Phoenix cluster is buzzing with stars that are forming about 20 times faster than in the Perseus cluster.
This rate is the highest seen in the centre of a galaxy cluster, NASA said.
However, the frenetic pace of star birth and cooling of gas in the Phoenix cluster which are causing the galaxy and the black hole to add mass very quickly, are going to be short-lived, predict the astronomers.
"The galaxy and its black hole are undergoing unsustainable growth. 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," said co-author Bradford Benson, of the University of Chicago.
Interestingly, the Phoenix cluster and its central galaxy and supermassive black hole are already among the most massive known objects of their type in the cosmos.
Because of their tremendous size, galaxy clusters are crucial objects for studying cosmology and galaxy evolution, hence finding one with such extreme properties like the Phoenix cluster is important. The new discovery may force astronomers to rethink how these colossal structures and the galaxies that inhabit them evolve in the Universe.
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