Mapping the universe then and now

It's a slow, palm-moistening drive up the one-lane dirt road that clings to the steep contours of Mt. Hopkins, 35 miles south of Tucson, Ariz.

Creeping along in a small car, it's hard to imagine how a tractor-trailer truck bearing a fragile, 21-foot-diameter mirror could ever clear the hairpin turns to reach the glistening white telescope perched atop the 8,500-foot summit.

With its new, larger mirror to gather more light and some new instruments, the refurbished telescope is slated to become a powerful tool in one of modern astronomy's most ambitious efforts: to build 3-D maps of the observable universe. Using mountaintop telescopes worldwide, teams of astronomers are picking slices of the night sky and mapping as many galaxies as weather, instruments, and funding allow. Underlying these efforts is a "drive to explore and write your address in the long form. The first step in knowing or understanding is to have a map. Nearly everything we do in science, we first need a picture," explains Margaret Geller, an astronomer at the Harvard-Smithsonian Center for Astrophysics (CFA) in Cambridge, Mass., which oversees the observatory on Mt. Hopkins. It has been a center for cosmic cartography for more than 20 years.

Looking at ever-more distant objects in the universe means looking back in time, so the maps, and the information needed to build them, contain a wealth of clues about the structure and evolution of the universe.

Last week, for example, a team of astronomers using the 3.9-meter Anglo-Australian Telescope in New South Wales, Australia, released a 3-D map containing more than 100,000 nearby galaxies, a population four times larger than any previous survey. Their goal is to gather data on 250,000 galaxies.

Like its predecessors, the new survey shows galaxies gathered into enormous superclusters stretched out into thin corridors of light separated by vast, empty regions as much as 200 million light-years across.

"To see the scales of structure is interesting, but it's not telling us anything new. The real objective is to measure clusters of galaxies at high precision and in a lot of detail," says collaborator David Weinberg, an associate professor of astronomy at Ohio State University.

Such data, he continues, can provide critical tests of existing theories or open up new views of what the early universe was like, how galaxies and their stars form and evolve, and help refine values for such critical cosmological factors as the density of matter in the universe.

Using data from the new survey, the project's researchers concluded that all of the matter in the universe - the "normal" matter we can see because it gives off radiation, and the "dark" matter we don't see, but which keeps galaxies and clusters of galaxies from flying apart as they rotate - falls far short of what's needed to halt the universe's expansion.

The results, according to Johns Hopkins University astrophysicist Karl Glazebrook, point to a universe in which two-thirds of the energy driving the expansion come from "vacuum energy," a form of energy predicted by quantum physics. Under this scenario, he notes, the universe will expand forever, and at an increasing speed.

Efforts to map the distribution of galaxies began in the 1950s, when it was still fashionable to call galaxies nebulae. Follow-up surveys found clusters of galaxies and the local supercluster, but the surveys weren't large enough or deep enough to reveal anything larger, Dr. Geller explains.

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