A string of ancient galaxies has thrown astronomers for a loop by defying standard predictions for the evolution of the universe. The colossal structure hints at possible misunderstandings of how the universe, or maybe mysterious dark matter, behaved shortly after the universe was born.
This is a computer artist's illustration of a giant but remote galaxy string discovered recently. The fuzzy, bright areas in the cube represent galaxies discovered about 10.8 billion light-years away in the direction of the southern constellation Grus (the Crane). Click to enlarge.
THEORY: Computer model of the early universe. Gravity arranges matter in thin filaments. High-density regions (yellow) undergo collapse and ignite bursts of star formation. These proto-galaxies stream along the filaments (red shows medium density) and meet at nodes, causing a buildup of galaxies. Low-density areas are blue.
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The arc of galaxies is arranged in an easily defined, gravitationally bound superstructure. But it's so old -- forming just 2.8 billion years after the Big Bang -- that astronomers aren’t sure how it had enough time to develop.
While the modern universe is full of galaxy clusters, it should not have been that way so long ago.
"This is the earliest and largest structure of galaxies that we have ever seen," said Povilas Palunas, an astronomer with the University of Texas and lead author of a report on the study. "And we find it’s a discrepancy with what all models predict for the early universe."
Astronomers have long held what they call a hierarchical view of the universe in which dark matter -- invisible stuff up that makes up 90 percent of the material in the universe -- collected in clumps, attracting the interstellar gas that formed the first stars about 200 million years after the Big Bang. Those stars collected into galaxies, which themselves grouped into clusters and later giant galactic strings.
Some theorists have likened the setup to a spider web, with water drops representing normal matter and sliding toward nodes of the web.
But the process is thought to have taken billions of years, and supercomputer simulations of the early universe predict that such large-scale structures would not be able to form as fast as the newfound string apparently had come together.
"The universe is growing faster than we thought," Palunas said.
The research is set to appear in a February issue of the journal Astrophysical Letters and was presented by Palunas and his colleagues earlier this month at the 203rd meeting of the American Astronomical Society (AAS) in Atlanta.
Palunas and a team of astronomers said the string of galaxies stretches across the Southern Hemisphere sky in the constellation Grus (the Crane). Its sits about 10.8 billion light-years away, and with a length of 300 million light-years and a width of 50 million light-years, the string is the biggest structure of its era, Palunas said.
One light-year equals the distance traveled by light in a year, about six trillion miles or 9.5 trillion kilometers.
Using a pair of ground telescopes, the astronomers detected 37 bright galaxies and a quasar -- a superbright galaxy in the making -- within the string, but suspect it may contain thousands more.
"We're seeing just the tip of the iceberg, only a few of the brightest galaxies," said astronomer Gerard Williger of Johns Hopkins University, another team member. "We're pretty sure there are a lot of faint galaxies that we haven't seen or counted yet."
A more in-depth study with larger telescopes and longer image-exposure times could be useful in detecting those dimmer objects, he added.
The 156-inch (4-meter) Blanco Telescope in Chili originally detected the galaxy string and was supported by observations with the 154-inch (3.9-meter) Anglo-Australian Telescope in Eastern Australia.
A Matter that's Dark
The existence of the galactic string seems to fall in line with other recent discoveries of earlier-than expected galaxies. During the AAS meeting, for example, astronomers with the Gemini Deep Survey announced their study of old, massive galaxies in the early universe.
"We do know that things like this should form eventually," said Harry Teplitz, a member of the Gemini observation team from Caltech. "They eventually fall into great sheets and walls like the Great Wall." The Great Wall is a large mass of galaxies 250 million light-years distant that was first discovered in 1989 by astronomers John Huchra and Margaret Geller.
Researchers with the galactic string study said it is possible that dark matter may have behaved differently in the distant past -- not collecting in clumps as expected today -- a setup that may have allowed the great string to form while others did not. There also may be something inherently missing from today's models of universe evolution, they added.
Or Maybe Not
Despite the new reports, astronomer Robert Kirshner, a professor with the Harvard-Smithsonian Center for Astrophysics, said it was too early to turn away from current hierarchical models of the universe.
"I wouldn't panic yet," said Kirshner, who was not part of the new study. The string "is just one observation, and it could be of a very extreme place in the universe," he said, adding that the finding is just the beginning of a growing understanding of structure in the universe.
Researchers said that one of the first steps to understanding the giant string is to look at an even larger swath of sky to determine if there is an even larger galactic structure at work. An area 10 times the size of the current study, they said, should be a sufficient start.
"What we also have to do now is work hand-in-hand with the theorists," said Williger of Johns Hopkins, adding that larger and more updated universe models will be key resources for researchers as they move forward.
I had to fix a typo in that one. If you read down you'll see Anglo-Australian Telescope, it was Anglo-American Telescope which is completely false.
This is a great find. We find something great each day.