The most distant known galaxy cluster has been discoveredwith NASA's Chandra X-ray Observatory.
The cluster, known as JKCS041, is located about 10.2 billionlight-years away and is observed as it was when the universe was only about aquarter of its present age. It beats the previous record holder, XMMXCSJ2215.9-1738, by about a billion light-years.
Galaxy clusters ? clumpings of galaxies held together bymutual gravitational attraction ? are the largestgravitationally bound objects in the universe. Finding such a largestructure at this very early epoch can reveal important information about howthe universe evolved at this crucial stage.
JKCS041 is found at the cusp of when scientists think galaxyclusters began to exist in the early universe based on how long it should takefor them to assemble. Therefore, studying its characteristics ? such as composition,mass, and temperature ? will reveal more about how theuniverse took shape.
"This object is close to the distance limit expectedfor a galaxy cluster," said Chandra team member Stefano Andreon of theNational Institute for Astrophysics in Milan, Italy. "We don?t thinkgravity can work fast enough to make galaxy clusters much earlier."
The component galaxies of JKCS041 were originally detectedin 2006 in a survey from the United Kingdom Infrared Telescope (UKIRT). Thedistance to the cluster was then determined from optical and infraredobservations from UKIRT, the Canada-France-Hawaii Telescope in Hawaii, and NASA?s Spitzer Space Telescope.
The Chandra data were the final ? but crucial ? piece ofevidence that showed that JKCS041 was, indeed, a genuine galaxy cluster. Theextended X-rayemission seen by Chandra shows that hot gas has been detected between thegalaxies, as expected for a true galaxy cluster rather than one that has beencaught in the act of forming.
It is not yet possible, with the detection of just oneextremely distant galaxy cluster, to test cosmological models, but searches areunderway to find other galaxy clusters at extreme distances.
"This discovery is exciting because it is like findinga Tyrannosaurus rex fossil that is much older than any other known,"said team member Ben Maughan, from the University of Bristol in the United Kingdom. "One fossil might just fit in with our understanding of dinosaurs, butif you found many more, you would have to start rethinking how dinosaursevolved. The same is true for galaxy clusters and our understanding ofcosmology."
The finding will be detailed in an upcoming issue of thejournal Astronomy & Astrophysics.