The most distant galaxy cluster yet has been discovered by combining data from NASA's Chandra X-ray Observatory and optical and infrared telescopes.

The cluster 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.

JKCS041 is found at the cusp of when scientists think galaxy clusters can 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 Stefano Andreon of the National Institute for Astrophysics (INAF) in Milan, Italy. "We don't think gravity can work fast enough to make galaxy clusters much earlier."

Distant galaxy clusters are often detected first with optical and infrared observations that reveal their component galaxies dominated by old, red stars. JKCS041 was 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. Infrared observations are important because the optical light from the galaxies at large distances is shifted into infrared wavelengths because of the expansion of the universe.

The Chandra data were the final - but crucial - piece of evidence as they 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.

Also, without the X-ray observations, the possibility remained that this object could have been a blend of different groups of galaxies along the line of sight, or a filament, a long stream of galaxies and gas, viewed front on. The mass and temperature of the hot gas detected estimated from the Chandra observations rule out both of those alternatives.

"This is a composite image of the most distant galaxy cluster yet detected. This image contains X-rays from NASA's Chandra X-ray Observatory, optical data from the Very Large Telescope (VLT), and optical and infrared data from the Digitized Sky Survey. This record-breaking object, known as JKCS041, is observed as it was when the Universe was just one quarter of its current age. X-rays from Chandra are displayed here as the diffuse blue region, while the individual galaxies in the cluster are seen in white in the VLT's optical data, embedded in the X-ray emission. (Credit: X-ray: NASA/CXC/INAF/S.Andreon et al Optical: DSS; ESO/VLT)"

Source: Chandra X-ray Center