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.
advertisement
