Mathematics

Cosmologists from the University of Portsmouth have helped discover the most distant cluster of galaxies ever found. The cluster may be the most massive yet seen at such an early era in the Universe. Professor Bob Nichol of the Institute of Cosmology and Gravitation will be interviewed this evening (06 June 2006) on the Radio 4 programme The World Tonight.

The discovery was announced this week at the 208 th American Astronomical Society meeting in Calgary.

"The key question now is: What?s it doing there?" said Professor Bob Nichol, of the Institute of Cosmology and Gravitation at the University of Portsmouth, co-author on the paper.

"This massive lump of dark matter is three-quarters of the way back to the Big Bang."

Almost 10 billion light years from Earth, cluster XMM-XCS 2215-1734 contains hundreds of galaxies surrounded by superheated, X-ray-emitting gas at more than 10 million degrees. The XMM Cluster Survey (XCS) team used observations from the European X-ray Multi Mirror (XMM) Newton satellite to discover this new cluster and then determined its distance using the 10-meter W. M. Keck telescope in Hawaii.

I couldn't believe it when I saw that this distant cluster appears to be full of old galaxies, said lead author Professor Adam Stanford, a research scientist at UC Davis and at the Lawrence Livermore National Laboratory.

"It is a fossil of the early Universe and therefore will be treasured by all astronomers. It's a challenge for our models of the way massive galaxies formed, and to our understanding of how such massive clusters could exist at a relatively early era in the Universe.

XMM-XCS 2215-1734 is surprisingly large. Using the temperature of the X-ray emitting gas, Kivanc Sabirli, a graduate student at Carnegie Mellon University, determined that the cluster is approximately 500 trillion times the mass of our Sun. Most of the mass is "dark matter," a mysterious form of matter that dominates the mass of all galaxies and clusters in the Universe but cannot be seen by our telescopes.

The team is embarked on a long-term observing program to find hundreds more clusters, using telescopes in Chile, Arizona and Hawaii.

The team includes: Michael Davidson and Robert G. Mann, University of Edinburgh, U.K.; Matt Hilton and Chris A. Collins, Liverpool John Moores University, U.K.; Pedro T.P. Viana, Universidade do Porto, Portugal; Scott T. Kay, Oxford University, U.K.; Andrew R. Liddle, University of Sussex, U.K.; Christopher J. Miller, National Optical Astronomy Observatory, Tucson; Robert C. Nichol, University of Portsmouth, U.K.; Michael J. West, University of Hawaii and the Gemini Observatory, Chile; Kivanc Sabirli, Carnegie Mellon University; S. Adam Stanford, UC Davis and Lawrence Livermore National Laboratory; Christopher J. Conselice, University of Nottingham, U.K.; Hyron Spinrad, UC Berkeley; Daniel Stern, Jet Propulsion Laboratory; and Kevin Bundy, California Institute of Technology. The work was funded by NASA, the Particle Physics and Astronomy Research Council (U.K.), the Hosie Bequest, and the National Science Foundation.

Institute of Cosmology and Gravitation.

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