Galactic supercluster discovered

The discovery of the largest known structure in the universe - a string of galaxies stretching 700 million light-years across the Milky Way - could help researchers trace the evolution of the universe.

The discovery, announced by the National Science Foundation, was made by Dr. Riccardo Giovanelli, a staff researcher at the National Astronomy and Ionosphere Center near Arecibo, Puerto Rico, and Dr. Martha Haynes, assistant director of the National Radio Astronomy Observatory in Green Bank, W.Va.

Dr. Giovanelli told the Los Angeles Times the discovery challenges one theory of the origin of galaxies and the assumption that matter is distributed evenly throughout the universe.

''The largest clumps of matter in the universe, until a few years ago, were thought to be clusters of galaxies with size of about 20 million to 30 million light-years and more or less of spherical structure,'' Dr. Giovanelli said. ''They now appear to be filamentary in nature, elongated, and at least 10 times larger than previously thought.'' (A light-year is the distance light travels in one year at a speed of 186,000 miles a second.)

One theory of the origin of matter says that galaxies form first, then, with gravity, merge into galaxy clusters that grow bigger as the universe ages. But the latest findings suggest the galaxies condensed from the filamentary structures (estimated to contain 1 million billion stars), which are much too big to have come about through gravitational clustering.

''If you consider the time needed to travel from one end of this supercluster to the other, it would be much larger than the age of the universe. Superclusters came first, and galaxies came later,'' Dr. Giovanelli said.