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Probing a universe of bubbles and voids.

Probing a universe of bubbles and voids

The distribution of galaxies in the universe appears far from uniform. Astronomers see large numbers of galaxies concentrated in superclusters and in sheets, or "walls," accompanied by neighboring "voids" holding significantly smaller galactic populations. Researchers now have amassed additional evidence that the universe may have a bubbly or sponge-like structure, featuring clumps of galaxies typically separated by distances on the order of 400 million light-years.

Alexander S. Szalay of Johns Hopkins University in Baltimore and his collaborators initially determined the positions of galaxies along a long, narrow line of sight -- a pencil beam -- in the direction of the Milky Way's north and south galactic poles. The pencil-beam survey suggested that over a distance of 7 billion light-years, galaxies appear in clumps spaced about 420 million light-years apart (SN:5/5/90, p.287).

To check this surprising result, the team measured the distances to galaxies along two additional lines of sight at 45[degrees] to the original direction. Again they detected concentrations of galaxies separated by distances of roughly 400 million light-years. Preliminary, partial results from pencil-beam surveys in other directions show similar galaxy distributions.

"Galaxies come in fairly obvious clumps," Szalay says. He described his group's findings last week at an astrophysics meeting in College Park, Md., titled "After the First Three Minutes."

At the same time, the new results fail to support initial indications that walls of galaxies may fall into a regular pattern. Instead, the positions and spacing of clumps vary from one line of sight to another. "One can see walls, but they're not evenly spaced," Szalay says.

The pencil-beam surveys probe deeper into the universe than any other survey of galaxy positions. Along the way, they pick up known concentrations of galaxies, including several local superclusters and a sheet of galaxies now termed the "Great Wall" (SN: 11/25/89, p.340).

"This is an exciting result," says Neta Bahcall of Princeton (N.J.) University. "So far, the pencil-beam surveys and supercluster catalogs fit together very well."

However, the surveys of galaxy positions completed so far haven't completely ruled out the possibility that astronomers may yet identify coherent patterns and structures in the distribution of galaxies on considerably larger scales.
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Title Annotation:distribution of galaxies
Author:Peterson, Ivars
Publication:Science News
Date:Oct 27, 1990
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