The most distant - and oldest - galaxy cluster yet has been discovered, beating the previous record holder by about a billion light years.
The cluster, known as JKCS04, was found by combining data from NASA's Chandra X-ray Observatory and optical and infrared telescopes. It is located about 10.2 billion light years away, and can be seen as it was when the Universe was only about a quarter of its present age.
Galaxy clusters 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.
"This object is close to the distance limit expected for a galaxy cluster," said Stefano Andreon of the National Institute for Astrophysics in Milan. "We don't think gravity can work fast enough to make galaxy clusters much earlier."
JKCS041 was originally detected in 2006 in a survey from the United Kingdom Infrared Telescope. The distance to the cluster was then determined from optical and infrared observation. The Chandra data were the final - but crucial - piece of evidence as they showed that JKCS041 was, indeed, a genuine galaxy cluster.
It isn't 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.
"What's exciting about this discovery is the astrophysics that can be done with detailed follow-up studies," said Andreon.