The most distant known galaxy cluster has been discovered with NASA's Chandra X-ray Observatory.
The cluster, known as JKCS041, is located about 10.2 billion light-years away and is observed as it was when the universe was only about a quarter of its present age. It beats the previous record holder, XMMXCS J2215.9-1738, by about a billion light-years.
Galaxy clusters ? clumpings of galaxies held together by mutual gravitational attraction ? are the largest gravitationally bound objects in the universe. Finding such a large structure at this very early epoch can reveal important information about how the universe evolved at this crucial stage.
JKCS041 is found at the cusp of when scientists think galaxy clusters began to exist in the early universe based on how long it should take for them to assemble. Therefore, studying its characteristics ? such as composition, mass, and temperature ? will reveal more about how the universe took shape.
"This object is close to the distance limit expected for a galaxy cluster," said Chandra team member Stefano Andreon of the National Institute for Astrophysics in Milan, Italy. "We don?t think gravity can work fast enough to make galaxy clusters much earlier."
The component galaxies of JKCS041 were originally detected in 2006 in a survey from the United Kingdom Infrared Telescope (UKIRT). The distance to the cluster was then determined from optical and infrared observations from UKIRT, the Canada-France-Hawaii Telescope in Hawaii, and NASA?s Spitzer Space Telescope.
The Chandra data were the final ? but crucial ? piece of evidence that showed that JKCS041 was, indeed, a genuine galaxy cluster. The extended X-ray emission seen by Chandra shows that hot gas has been detected between the galaxies, as expected for a true galaxy cluster rather than one that has been caught in the act of forming.
It is not yet possible, with the detection of just one extremely distant galaxy cluster, to test cosmological models, but searches are underway to find other galaxy clusters at extreme distances.
"This discovery is exciting because it is like finding a 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, but if you found many more, you would have to start rethinking how dinosaurs evolved. The same is true for galaxy clusters and our understanding of cosmology."
The finding will be detailed in an upcoming issue of the journal Astronomy & Astrophysics.