Blown away: froth of cosmic bubbles.

Blown away: Froth of cosmic bubbles

Astronomers used to think the universe was homogeneous. But recent observations of voids in the universe, of clusters of galaxies associated in ultralong superclusters, have seemed to fault the idea. Soon astronomers may have to give it up entirely. The latest, and apparently most extensive, observation, reported at last week's meeting in Houston of the American Astronomical Society, indicates that the universe is a froth of bubbles, large empty volumes with galaxies clustered in their walls.

The distribution of galaxies was observed in what the scientists call a "slice of the universe,' a region extending almost halfway around the horizon and 6| thick. In this they have plotted the locations of galaxies according to their velocities of recession from us. The third dimension has to be velocity, says Margaret J. Geller of the Harvard-Smithsonian Center for Astrophysics (CFA) in Cambridge, Mass., because, although astronomers are agreed that a galaxy's recession velocity measures its relative distance, they cannot agree on the value of the Hubble constant, by which they could calculate absolute distance. Along with Geller, the researchers include Valerie de Lapparent (visiting from the Ecole Normale Superieure de Jeunes Filles and the University of Paris VII in France) and John P. Huchra of the Harvard-Smithsonian CFA.

The evidence shows up in the pattern in the above illustration: Galaxies appear clustered in long strings with open spaces between them. This is what would appear on a slice taken through a collection of soap bubbles: The lines would be the projections of the walls of the bubbles on the slice. So de Lapparent, Geller and Huchra propose that the universe is structured like soap bubbles. Such a structure could be explained by a theory proposed in 1981 by Jeremiah P. Ostriker of Princeton (N.J.) University and Lennox L. Cowie of the University of Hawaii, which, as Geller says, was generally ignored at the time. According to that theory, a primordial generation of stars, formed before any galaxies, would have exploded. The force of the explosions would have emptied out these bubbles. The formation and expansion of the bubbles is superimposed upon the general (Big Bang) expansion of the universe. Combined observations of both expansions could be one way of pinning down the value of the Hubble constant, Geller says.

The observers plan deeper surveys. "Depth' refers to the faintest galaxies recorded. These may be either the farthest out (and if so their recession velocities will indicate that) or the faintest (intrinsically) that can be recorded at any intermediate distance. A deeper survey should tell whether the bubble pattern extends farther out in the universe. It should also tell whether, as intrinsically fainter galaxies are taken into account, the bubble pattern persists at closer distances.