Astronomers using ground and space telescopes have found a pair of galaxy clusters that may shed light on when the first galaxies began to form in the early universe.
Their findings, the researchers say, support the theory that galaxies began to take shape while the universe was still young.
The first cluster, a massive collection of possibly thousands of faint galaxies, formed when the universe was only five billion years old, about a third its current age, researchers said. Current estimates place the age of the universe at about 13.7 billion years old.
"Until recently people didn't think that clusters existed when the universe was only about five billion years old," explained John Blakeslee of Johns Hopkins University in Baltimore, Maryland. Blakeslee led the study on the galactic cluster, called RDCS1252.9-2927, which was the most massive cluster in its epoch. The research appeared in the Oct. 20 issue of the Astrophysical Journal.
The second galaxy cluster is actually a proto-cluster, containing a clutch of "infant galaxies" that existed just 1.5 billion years after the Big Bang. Small developing galaxies surround the center of the cluster, where a massive embryonic galaxy is emitting spectacular radiowave jets fueled by a supermassive black hole. It was these radio-jets that led radio astronomers to hunt for the smaller developing galaxies in the proto-clusters.
"Massive clusters are the cities of the universe, and the radio galaxies within them are the smokestacks we can use for finding them when they are just beginning to form," said astronomer George Miley of the Leiden Observatory in the Netherlands. Miley led the study on the proto-cluster, which is dubbed TNJ1338-11942. The research will appear in the Jan. 1, 2004 issue of the journal Nature.
Both studies used the Advanced Camera for Surveys (ACS) aboard the Hubble Space Telescope (HST) to image the galaxy clusters as part of a coordinated effort by the ACS science team to track the formation and evolution of galaxy cluster over long spans of time. Further observations with the NASA's Chandra X-ray Observatory and the European Space Agency's XMM-Newton X-ray instrument helped researchers determine the mass contained within the clusters. The results of the two studies led participating astronomers to believe that their galaxy clusters were the progenitors of more recent galaxy clusters seen today.
"The cluster RDCS1252 looks like a present-day cluster," said astronomer Marc Postman of the Space Science Telescope Institute that runs the HST. Postman is also co-author on both of the galaxy cluster studies. "In fact, if you were to put it next to a present day cluster you wouldn't know which is which."
The ACS team hopes to expand its understanding of galaxy formation by conducting near-infrared observation on clusters to examine formation, and by probing ultra-distant radio galaxies for more proto-galaxies.
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