Lumps, clumps and jumps in the universe.

Lumps, clumps and jumps in the universe

Astronomers have already discovered lumps, motion and structure never suspected in a universe once considered smooth and expanding uniformly in all directions (SN: 3/22/86, p. 182). Two researchers now say the universe is even lumpier, has faster relative motion and shows larger structures than previously believed.

Neta Bahcall of the Space Telescope Science Institute in Baltimore and Raymond Soneira, previously of the Institute for Advanced Study in Princeton, N.J., searched for large-scale structures in the universe by tracing superclusters -- clusters of clusters of galaxies, each containing hundreds of billions of stars. The astronomers looked at the light spectra emitted by 175 galaxy clusters. As the clusters speed away from Earth, their spectral emissions shift toward the infrared region of the spectrum; the amount of shift indicates the speed of movement away.

The researchers then used three statistical methods to interpret the cluster velocities. They established that clustering occurs, determined the spatial relationships between clusters in a supercluster and showed how the superclusters actually look. Says Soneira, "All three methods produced the same results."

But those results to be published in the ASTROPHYSICAL JOURNAL later this year -- were unexpected, says Bahcall, and "very exciting.... Our whole view of the universe is changing right in front of us." The new view includes:

* Much more extensive clumping of galaxy clusters, and much larger clumps, than had been expected. It now appears that superclusters can extend as far as 500 million light-years, about 1 percent of the known universe.

* Relative motion within superclusters of 2,000 kilometers per second more than then speed accounted for by the general expansion of the universe, and about 5 times more than the speed expected as a result of gravitational motion.

These discoveries are the latest in a series of findings defying the theory that the universe is expanding smoothly and uniformly. Forces other than the Big Bang may cause the clumpiness and the motion. "Probably the same force that created the superclusters is the force that propels them," says Bahcall, but she adds that "we have no good model at the moment" to explain the existehce or the motion of the clusters.

Three main theories make the attempt. One proposes that superclusters emerged soon after the Big Bang as results of large fluctuations in the overall smoothness of the primordial universe. Over time, the superclusters fragmented to form galaxy clusters that early galaxies exploded, propelling clusters at the high speeds observed.

An equally promising theory, according to Bahcall, postulates that small fluctuations in the smooth early universe coalesced into galaxies under their own gravitational pull; later, gravity pulled galaxies together into clusters and superclusters. not enough time has passed, however, for gravity alone to have formed the large structures now seen, says Bahcall. This leads to speculation that huge clumps of dark matter (black holes, neutrinos or other invisible matter) may help pull the galaxy clusters along.

Perhaps the real answer incorporates a little of each approach. Says Bahcall, "We're trying to combine them in some physical way. I think it's probably more complicated than any one [explanation]."

Even more tantalizing for Bahcall is the possibility that the cigar-shaped superclusters are subsections of still larger, filamentlike structures expending across the entire universe. "My feeling," she says, "is the more we study large-scale structures, the more we'll see even larger structures."