This Hubble Space Telescope image shows a cluster of galaxies.
Largest ever survey of distant galaxy groups
3 Jul 2009
An international team of researchers has completed the largest ever survey designed to find very distant clusters of galaxies.
Named the Spitzer Adaptation of the Red-sequence Cluster Survey, or "SpARCS", it used "deep" ground-based optical observations from the Cerro Tololo InterAmerican Observatory 4-metre telescopes and Canada-France-Hawaii Telescope 3.6-metre telescope, combined with Spitzer Space Telescope infrared observations.
In a universe thought to be 13.7 billion years old, SpARCS is designed to identify the clusters as they appeared when the universe was just six billion years old or younger.
Clusters of galaxies are rare regions of the universe consisting of hundreds of galaxies containing trillions of stars, plus hot gas and mysterious dark matter. Most of the mass in clusters is actually in the form of invisible dark matter, which astronomers are convinced exists because of its influence on the orbits of the galaxies.
< One of the most distant galaxy clusters ever discovered, seen when the universe was a mere 4.8 billion years old. Each of the red blobs is a galaxy.
An example of one of the most massive clusters found in the SpARCS survey is shown in the image at left. Seen when the universe was a mere 4.8 billion years old, this is also one of the most distant clusters ever discovered. Each of the red blobs is a galaxy within the cluster (the green blobs are just foreground stars within our own galaxy, The Milky Way).
"We are looking at massive structures very early in the universe's history," said Gillian Wilson, an associate professor of physics and astronomy at the University of California-Riverside who leads the SpARCS project.
The SpARCS survey has discovered about 200 possible new clusters.
"It is very exciting to have discovered such a large sample of these rare objects," Wilson said. "Although we are catching these clusters at early times, we can tell by their red colours that many of the galaxies we are seeing are already quite old."
"We will be following up this new sample for years to come, to better understand how clusters and their galaxies form and evolve in the early universe," she said.
Adapted from information issued by UC Riverside / Image courtesy G. Wilson (UC Riverside) and A. Muzzin (Yale).
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