Galaxy cluster’s maturity surprises scientists

CALGARY, Alberta - A ghostly blue blob amid a swarm of red dots in a new cosmic image is the superhot intergalactic gas permeating the space within the most distant cluster of galaxies found to date.

Located nearly 10 billion light years away, Cluster XMMXCS 2215-1738 is described by its discoverers as a tantalizing glimpse of what galaxy clusters were like at their earliest stages of formation.

Individual galaxies have been detected at greater distances. But the newly discovered cluster contains several hundred galaxies bound together by mutual gravitational attraction.

The finding was announced here this week at the 208th meeting of the American Astronomical Society.

Young and old
A light-year is the distance that light can travel in a year, so the light from this cluster took almost 10 billion years to reach us. Since the universe is thought to be 13.7 billion years old, the record-setting cluster must have formed when the universe was relatively young.

"Yet this distant cluster appears to be full of old galaxies," discovery team member Adam Stanford noted with amazement.

Stanford and his colleagues said the total mass of the cluster is enough to contain 500 trillion stars comparable in mass to our Sun. That's a surprising stellar mass for a galaxy cluster to have achieved at such an early era in the evolution of the universe, said Stanford, a researcher at the University of California, Davis, and at Lawrence Livermore National Laboratory.

'Hot' finding
Stanford and the other members of the XMM Cluster Survey, an international team of astronomers, made their discovery by combining X-ray observations from the European X-ray Multi Mirror (XMM) Newton satellite with optical observations using the 10-meter W.M. Keck telescope on Mauna Kea, Hawaii.

Intergalactic gas in the record-setting cluster glows with powerful x-ray emissions at a temperature of 10 million degrees, said team member Robert Nichol, from the University of Portsmouth, England. That's what made the detection of this distant cluster possible, says Nichol. It also makes this a "hot" find in every sense of the word, since this is the hottest cluster yet found at an extreme distance.

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