Biggest Galaxy Gang From Young Universe Seen

A massive galaxy cluster located 7 billion light-years from Earth. This cluster weighs as much as 800 trillion suns. Galaxies with "old" stellar populations, are circled in yellow; galaxies with "young" stellar populations, are circled in blue.



Astronomers on the hunt for the biggest, most distant gangs of galaxies have landed a prize catch, a behemoth of a cluster 800 trillion times more massive than the sun ferreted out by a new cosmic fishing net from when the universe was half its present age.
The galaxy cluster, known as SPT-CL J0546-5345, is so far away that its glow takes 7 billion light-years to reach us.
Astronomers like these oddball giants because they show what happens in the most richly dense parts of the universe. That information interests cosmologists trying to work out how the universe came to exist and the role of dark energy in fueling its growth, as well as to observational astronomers studying how galaxies formed.
So while some researchers are delving into the contents and geometry of SPT-CL J0546-5345, others are still fishing, especially since the new technique that netted the über-cluster proved so successful.
Credit for the catch goes to the South Pole Telescope, one of three observatories designed to detect distortions in the ubiquitous shimmer of radiation emanating from the Big Bang creation event. The telescopes sift through the background cosmic radiation to find spots where it has been slightly perturbed as it passes through extremely hot gas, a hallmark characteristic of galaxy clusters.
"The cosmic microwave background has been our most important source of information about the geometry and contents of the universe," astronomer Charles Lawrence, with NASA's Jet Propulsion Laboratory in Pasadena, Calif., told Discovery News.
X-ray telescopes can detect this gas, but finding targets has been a hit-or-miss proposition. Sky surveys under way by the South Pole Telescope, the Atacama Cosmology Telescope in Chile and the Planck space observatory, all of which mine the cosmic background rays, are changing the paradigm.
The discovery of SPT-CL J0546-5345 and its confirmation as the most massive galaxy cluster ever found at 7 billion light-years -- a time/distance boundary known in scientific parlance as "redshift 1" -- shows that these new types of surveys are successful, says astronomer Mark Brodwin, with the Harvard-Smithsonian Center for Astrophysics.
"Really massive clusters are really, really rare, so you have to cover a lot of area of the sky if you want to find some," Brodwin told Discovery News. "These surveys are really working, they really find clusters above redshift of one,  and they find super interesting clusters. We've never found something this massive before."
In studies of galaxies, size matters.
"The mass of the cluster is a very important factor in how galaxies evolved and you want to find the most massive ones to see the most extreme ends of that relationship," Brodwin said.
The number and size of super-massive galaxy clusters also will be used to refine theoretical understanding of how the universe formed.
"It's fun to go and actually measure how many we find that are that massive and make a comparison because we might learn something about our theory. We might find that it doesn't agree. We find maybe more than you'd expect to find," Brodwin said.
Theoreticians will soon have much more observational evidence to work with. In addition to partial-sky surveys by the South Pole Telescope and the Atacama Cosmology Telescope, the Planck space observatory is undertaking a full-sky survey, with the first results due to be reported in January, said Lawrence, who oversees a NASA team working with the European Planck spacecraft.
Brodwin's research appears in the current issue of Astrophysical Journal.