|MadSci Network: Astronomy|
Thanks for your question! The Great Wall of galaxies is a large structure found in the nearby universe by Margaret Geller and John Huchra, two astronomers at the Harvard-Smithsonian Center for Astrophysics. (In fact, Margaret Geller is my thesis advisor!). Geller and Huchra decided to make a map of the local universe by using the redshifts of galaxies in order to find their distances. They discovered extremely large structures, some up to 300 million light-years across! They found big empty regions with very few galaxies and long threads or filaments of galaxies. Several of these galaxy threads are at about the same distance from us, so they seem to be part of a giant sheet of galaxies. The following is a quote from John Huchra's web page: "The structure running all the way across between 8 hours and 17 hours RA and 5,000 and 10,000 km/s is called the ``Great Wall,'' perhaps the largest single structure yet detected in any redshift survey. Its dimensions are about 600x250x30 million light years, sort of like a giant quilt of galaxies across the sky. (see Geller and Huchra 1989, Science 260, 1175.)". His site also has some pictures of the Great Wall.
Some astronomers use computers to try to simulate the history of the universe. They can make threads connecting knots of galaxies, but they still have trouble making big sheets like the Great Wall. Other astronomers are hard at work on new redshift surveys which look at much bigger volumes than the original survey of Geller and Huchra. These surveys will show how common sheets of galaxies are and if there are any sheets larger than the Great Wall. At least one of these surveys suggests that the Great Wall is one of the largest structures in the universe!
Sky and Telescope, August 1991, 137
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