Astronomers have detected the most distant galaxy cluster ever discovered lurking some 11.1 billion light-years away from Earth. Named CL J1001+0220 (CL J1001), the new find indicates that galaxy clusters were formed around 700 million years earlier than previously thought.
Galaxy clusters are thought to be the largest structures in the universe bound together by the force of gravity. The clusters can be comprised of anything from a handful, to hundreds of thousands of galaxies, and have been observed to vary greatly in terms of characteristics and galaxy distributions.
Prior to the new discovery, which was made using a host of ground and space based telescopes including Hubble, Chandra, and the ESO's Very Large Telescope, only loose protoclusters had been found so far away.
Astronomy is like cosmic archaeology, in that we never observe a heavenly body as it actually exists in the present day. Instead, we see it as it appeared when the light left its source. In the case of CL J1001, we are seeing the galaxy cluster as it was roughly 11.1 billion years ago.
The team behind the discovery believe that the light from CL J1001 left its source soon after it made the transition from a loose gathering of galaxies to a fully formed cluster, with a core consisting of 11 massive elliptical galaxies. This stage of evolution has never been seen before, and so could prove instrumental in updating models regarding the early evolutionary paths taken by galaxy clusters.
An analysis of the data showed that nine of the galaxies forming the core of CL J1001's were undergoing an impressive bout of star formation, with the equivalent of 3,400 Suns being created each year.
"This galaxy cluster isn't just remarkable for its distance, it's also going through an amazing growth spurt unlike any we've ever seen," says Tao Wang of the French Alternative Energies and Atomic Energy Commission (CEA) who led the study.
After comparing their data with advanced computer simulations designed to model the formation of galaxy clusters, the team discovered that CL J1001 was carrying a surprising amount of mass in the form of stars contained within the core galaxies.
This could suggest that current models are wrong regarding the rate of star birth in newly formed galaxy clusters, or that CL J1001 represents a rare form of cluster seldom seen, and therefore not accounted for in present theories.
The levels of star-birth could indicate that elliptical galaxies that form the cores of clusters experience bouts of star formation that are more intense, but also significantly more short-lived than those undertaken by their cousins existing outside of a cluster. The results also cast doubt on the prevailing theory that star birth in galaxies forming the core of a cluster takes place before the galaxy joins with the larger structure.
Moving forward, astronomers will attempt to discover further examples of clusters with characteristics similar to CL J1001, which will help determine whether these traits were common in the early universe, or some kind of cosmic fluke.
A paper describing the results is published in The Astrophysical Journal.
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