June 27, 2012
Researchers Make Celestial Observation, Despite Astronomical Odds
Lee Rannals for redOrbit.com
Astronomers were able to beat the odds by observing gravitational lensing taking place at 10 billion light-years away from Earth.
Gravitational lensing is the bending of light from a distant galaxy, and it has never been observed behind a cluster at this range before.
The giant arc is the stretched shape of a more distant galaxy whose light is distorted by the cluster's powerful gravity.
Astronomers reported in the July 10 issue of The Astrophysical Journal that they were able to observe the rare feat.
"When I first saw it, I kept staring at it, thinking it would go away," University of Florida astronomer Anthony Gonzalez, lead author of the study announcing the discovery, said in a press release. "The galaxy behind the cluster is a typical run-of-the-mill galaxy with a lot of young stars, but the galaxy cluster in front of it is a whopper for that range. However, it's really the way that the two systems are lined up that makes the occurrence truly remarkable."
The cluster's mass is noteworthy because it lays 10 billion light-years from Earth, meaning it was already in existence when the universe was just a quarter of its present age.
Astronomers believe that only a few of these clusters were even around when the universe was young, so finding the cluster itself is considered to be lucky.
"According to a statistical analysis, arcs should be extremely rare at that distance," Gonzalez said. "At that early epoch, the expectation is that there are not enough galaxies behind the cluster bright enough to be seen, even if they were 'lensed,' or distorted by the cluster."
"The other problem is that galaxy clusters become less massive the further back in time you go," he continued. "So it's more difficult to find a cluster with enough mass to be a good lens for gravitationally bending the light from a distant galaxy."
He said that finding the massive cluster at the range he had with a 9-square degree patch of sky that is also gravitationally lensing is a long shot, even if you were able to look into the whole sky.
"The chance of finding such a gigantic cluster so early in the universe was less than one percent in the small area we surveyed," team member Mark Brodwin of the University of Missouri-Kansas City said in a press release. "It shares an evolutionary path with some of the most massive clusters we see today, including the Coma cluster and the recently discovered El Gordo cluster."
According to Gonzalez, finding a cluster of that magnitude at that distance in such a small field of observation could mean that scientists have misunderstood exactly how many massive clusters were in existence 10 billion years ago.
"We just don't know," he said in the press release. "We need to find more clusters at this range so that we can get more data. So far we only have one example to study."
NASA said that finding this ancient gravitational arc may yield insight into how conditions were set up for the growth of clusters during the first moments after the Bing Bang.