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Why a galaxy far, far away has shattered records for birthing stars

Astronomers identify a giant cluster of galaxies 5.7 billion light-years from Earth. At its core new stars are being formed at a rate that could explain how supermassive black holes govern a galaxy's growth.

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Astronomers peering deep into the heart of a cluster of galaxies some 5.7 billion light-years away have found that the cluster’s central galaxy is producing stars at an extraordinary rate – up to hundreds of times more stars per year than any of its siblings in a handful of other well-studied clusters.

The largest, most productive galaxies in the universe are found at the centers of galaxy clusters, researchers say. And astronomers thought they had a pretty good handle on why these galaxies were at the top of the star-formation heap – acquisitions and mergers involving other galaxies.

The new find, however, in what the astronomers are calling the Phoenix Cluster, suggests an unexpected source of gas available to make new stars in these central galaxies – the gas between galaxies in the cluster.

Even more intriguing, it also could shed light on the interplay between supermassive black holes at the centers of galaxies and the galaxies themselves. That interplay is thought to limit the size each actor in this cosmic tug of war can reach.

As clusters go, the Phoenix Cluster is among the largest yet detected. The entire cluster spans some 8.5 million light-years. It contains hundreds of thousands of Milky Way-size galaxies, and sports an overall mass of 2,500 trillion suns. X-ray emissions from all of the hot gas it contains shine brighter than the X-ray emissions from any other known cluster.

The galaxy at the center of the Phoenix Cluster is "crushing the record" for star birth in galaxy clusters, says Michael McDonald, a researcher at the Kvali Institute for Astrophysics and Space Research at the Massachusetts Institute of Technology in Cambridge. Dr. McDonald is the lead author of the discovery's formal report, which appears in Thursday's issue of the journal Nature.

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