Galaxy map smooths out the vast cosmos.

Galaxy map smooths out the vast cosmos

Assembling 185 overlapping images of the sky like pieces of a cosmic mosaic, British astronomers have produced a map depicting a larger chunk of the universe than any other two-dimensional survey in the past. Though the ongoing survey has so far covered only about one two-thousandth the volume of the entire observable universe, it already includes a record 2 million galaxies, revealing some structural surprises while also confirming some familiar concepts.

Like others who have created smaller galactic maps, Will J. Sutherland, Steven J. Maddox and their colleagues at Oxford University found that the lumps and clumps formed by galactic clusters begin to smooth out over regions longer and wider than about 50 million light-years. But while previous work indicated a rapid smoothing of galactic distribution at this scale, the Oxford astronomers report that some lumpiness persists up to a scale of about 150 million light-years.

The team describes its findings, based on an analysis of galaxies contained in a cone-shaped region covering 10 percent of the sky's total area, in the April 15 MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY.

Sutherland says the new results may prompt researchers to revise or perhaps abandon some theories about the evolution of the universe, including the cold dark matter theory, which he contends cannot account for such large-scale lumpiness. At the same time, he adds, the survey supports other findings -- most notably the highly uniform glow of microwave background radiation left over from the Big Bang (SN: 4/21/90, p.245) -- that indicate all parts of the universe look essentially the same on a vast enough scale. Theorists already base their models on a universe with limited deviations from uniformity, but "this survey is the first reliable confirmation that the distribution of galaxies in the universe becomes uniform on large scales [beyond 150 light-years]," Maddox says.

Using a sequence of photographs of the southern celestial hemisphere taken by the UK Schmidt telescope at Siding Springs Observatory in New South Wales, Australia, the team picked out images of distant galaxies and discarded those of individual stars with the help of a computerized scanning machine. In contrast, a 1977 map analyzed by Princeton astronomers James E. Peebles and Edward J. Groth -- until now considered the largest galactic survey -- relied on data painstakingly evaluated by eye at Lick Observatory in northern California.

Astrophysicist Simon D.M. White of the University of Arizona in Tucson, who helped developed the theory of cold dark matter, says the new survey and other recent observations may indeed force revisions in his proposed scenario for the evolution of the universe. "Some people might say, 'If a theory can't describe [an observation], drop it,'" he told SCIENCE NEWS. "I'm more practical. I say, 'Try and revise it.'"

Sutherland says a recent statistical analysis indicates the newly mapped portion of the southern celestial hemisphere contains several sheets or walls of galaxies -- a phenomenon previously seen only in the northern hemisphere (SN: 11/25/89, p.340). The Oxford team plans to map the galactic distribution of nearly the entire sky, collaborating with researchers from Cambridge (England) University who are analyzing photographic plates from the Siding Springs Observatory and the Mt. Palomar Observatory in southern California.