Galactic beads on a cosmic string.

Galactic beads on a cosmic string

Imagine drilling a hole through the universe. At some points, the drill would pierce dense clumps of matter. Elsewhere, it would encounter little resistance as it passed through relatively empty regions. When astronomers determine the distances to galaxies along a long, narrow line of sight, they sample the distribution of matter in the universe in much the same way. They would likely see large numbers of galaxies at some points and few galaxies at others.

That's exactly what a team of astronomers in the United States and Great Britain recently found. However, they also discovered that over a distance of 7 billion light-years, the galaxies appear in regularly spaced clumps about 420 million light-years apart. The finding suggests that this particular line of sight happened to pierce a sequence of 13 evenly spaced "walls" of galaxies.

To get a sense of whether the observed periodicity represents a genuine pattern or merely a statistical fluke, researchers at the Lawrence Livermore (Calif.) National Laboratory and the University of California, San Diego, used simple computer models to study the kinds of patterns generated by various lines of sight through different distributions of matter. In their models, galaxies appear on the surfaces of bubbles or sheets in both random configurations and orderly cellular patterns.

The group's statistical analysis of where galaxies would appear along randomly oriented lines of sight seems to suggest that the most likely explanation for the observations is that all galaxies are arranged in a large-scale, regular pattern. A line of sight passing through a random pattern of bubbles has less than a 2 percent chance of producing the observed sequence, they conclude.

"The observations don't fit a random-cell pattern," says Livermore's Hannu Kurki-Suonio. But there's no good explanation for why galaxies would be arranged in a regular pattern. "If this regularity doesnht go away [in future surveys]," he says, "then the universe is really strange."