That Wall in China Is Nothing

24 October 2003 (All day)

Supersized. The new and old great walls (top and bottom).

Scientists have discovered the largest structure yet found in the universe, a "Great Wall" of galaxies 1.37 billion light-years long. This cosmic ribbon dwarfs anything seen before by more than 600 million light-years. The wall's vastness pushes the limits of existing cosmological theories, but astronomers say it won't break them.

Ever-deeper inspection of the sky has revealed a universe textured like a colossal sponge. Galaxies cluster into filaments or walls, separated by gigantic voids and tunnels. These structures, cosmologists say, originated in quantum fluctuations in the density of matter a split-second after the big bang.

A particularly impressive structure was found in 1989 by a team led by astronomers Margaret Geller and John Huchra. They dubbed it the Great Wall, because it's some 760 million light-years long, 200 million light-years wide, and 15 million light-years thick. For comparison, a single light-year is as long as 1.3 billion Great Walls of China. Scientists initially thought the Great Wall of Geller and Huchra was impossibly large to have formed under the influence of gravity, but computer simulations later revealed it fell within theoretical limits.

Investigators have now uncovered an even longer wall as part of the Sloan Digital Sky Survey, which is mapping 1 million galaxies across a quarter of the sky with telescopes at Apache Point Observatory in New Mexico. Astrophysicists J. Richard Gott and Mario Juric of Princeton University and colleagues report that the Sloan Great Wall is 80% longer than the Geller-Huchra Great Wall. Such a large feature shows up in about 10% of computer simulations of how the part of space they studied developed, which is why its size comes as a surprise to astrophysicists, but not as a death knell for their theories. The scientists have submitted their results to the Astrophysical Journal.

"It's a bit larger than we would have thought, but not embarrassingly so," Gott says. Astrophysicist Robert Kirshner of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, agrees that the new wall doesn't overturn existing theories. When the Sloan survey is finished, hopefully by 2005, it will be the most complete three-dimensional map of the universe ever. Gott says additional details about the Great Wall should help shed light on how the seeds of these walls and voids formed in the moments after the big bang.

Related sites
Sloan Maps of the Universe
Abstract of the paper
Huchra's Web site, detailing the discovery of the Geller-Huchra Great Wall

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