Magazine article Science News

Sound Waves May Drive Cosmic Structure

Magazine article Science News

Sound Waves May Drive Cosmic Structure

Article excerpt

The melody lingers on. Sound waves generated in the early universe may have helped orchestrate the striking pattern of galaxy clusters and huge voids seen in the sky today.

Many sky surveys have shown that galaxies and clusters of galaxies form a web stretching across hundreds of millions of light-years. In the Jan. 9 Nature, Jaan Einasto of the Tartu Observatory in Toravere, Estonia, and his colleagues provide new support for this picture. Analyzing a collection of data on galaxy clusters, they find evidence of a three-dimensional pattern of rich clusters and intervening voids with a nearly periodic spacing of about 390 million light-years.

These results, cautions Robert P. Kirshner of Harvard University, are open to question. The data are sketchy and the interpretation depends on details of how the galaxy clusters were selected for the analysis, he notes. Yet this and similar findings, including those from the detailed Los Campanas sky survey, clearly hint at the presence of structures as large as a few hundred million light-years, Kirshner adds.

Such architecture spells trouble for a popular theory of the growth of structure in the universe. Relying on a hypothetical, fast-moving type of invisible material known as cold dark matter, the theory predicts that the distribution of galaxies on large scales should be entirely random and so have no discernible pattern.

Without that theory, two possibilities remain, says Kirshner. Cosmologists might invoke some new type of physics, perhaps with a new type of subatomic particle, to explain how tiny fluctuations in the density of matter in the early universe developed into the cosmic architecture seen today. A simpler and less daring strategy, however, has been proposed by several researchers, including Alexander S. Szalay of Johns Hopkins University in Baltimore. These scientists suggest that acoustic oscillations-sound waves-generated when the universe was still a hot soup of protons and electrons left their imprint on ordinary matter, helping to determine its later structure.

Szalay explained the theory in Chicago last month at the Texas Symposium on Relativistic Astrophysics. …

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