Vast Cluster of Galaxies Spotted in Early Universe: Study

The newly discovered "proto-cluster" of galaxies, observed when the universe was only 1.7 billion years old (12 percent of its present age), is one of the most massive structures known at that distance.

"The protocluster will very likely grow into a massive cluster of galaxies like the Coma cluster, which weighs more than a quadrillion Suns," said Kyoung-Soo Lee, astrophysicist from Purdue University in the US.

Clusters this massive are extremely rare: only a handful of candidates are known at such early times. The new system is the first to be confirmed using extensive spectroscopy to establish cluster membership.

The team, led by Lee and Arjun Dey of the US National Optical Astronomy Observatory, used the Mayall telescope at the Kitt Peak National Observatory in Arizona to obtain very deep images of a small patch of sky, about the size of two full moons, in the constellation of Bootes.

The team then used the Keck II Telescope at the W M Keck Observatory on Mauna Kea to measure distances to faint galaxies in this patch, which unveiled the large grouping.

"Many of the faint galaxies in this patch lie at the same distance," said Dey. "They are clumped together due to gravity and the evidence suggests that the cluster is in the process of forming," he said.

Matter in the universe organises itself into large structures through the action of gravity. Most stars are in galaxies, which in turn collect in groups and clusters.

Galaxy clusters are commonly observed in the present-day universe and contain some of the oldest and most massive galaxies known.

The formation and early history of these clusters is not well understood. The discovery of young proto-clusters allows scientists to directly witness and study their formation.

The prevalence of massive clusters in the young universe can help constrain the size and expansion history of the universe.

The team is now searching larger areas of sky to uncover more examples of such young and massive protoclusters.

"The discovery and confirmation of one distant and very massive protocluster is very exciting," said Naveen Reddy, an astrophysicist at the University of California at Riverside. "But it is important to find a large sample of these so we can understand the possibly varied formation history of the population as a whole," Reddy said.

The research was published in the Astrophysical Journal.