Cosmic Error?

How old is the Milky Way? Astronomers have long considered it one of the older galaxies; Sir James Jeans deduced from its shape that the Milky Way (which includes the Earth) is probably in an advanced stage of senility. But this week one of the world's most eminent authorities on galaxies, Harvard's Professor Harlow Shapley, suggested that Sir James had it all backward. According to Shapley's theory, the Milky Way is in the first, not the last, stage of evolution.

Astronomers have observed that galaxies seem to come in four shapes: 1) spherical, 2) elliptical (like an egg), 3) tightly spiral (like a watch spring) and 4) loosely spiral (like a pinwheel). The Milky Way is a pinwheel. Sir James reasoned that a spherical galaxy spinning in space, like a whirling ball of soft butter, must spread out at the edges and flatten in the center and become more & more disk-shaped, thus evolving from a ball to a spiral. Therefore, said he, a sphere must be the first stage in galactic evolution and a spiral the last.

But Professor Shapley has noticed that spiral galaxies have many star clusters and star clouds -- a sign of youth, not age. A star cluster, he observed, is unstable. As it rotates, its stars, revolving at various speeds around the cluster's nucleus, are torn apart by "shearing forces" which break up the cluster and disperse the stars evenly through the galaxy.

Shapley further observed that spiral galaxies (especially the Milky Way) have many unstable, relatively short-lived supergiant stars, another sign of immaturity. Because spherical galaxies, on the other hand, have a smooth, stable structure with few star clusters and no supergiants, he concluded that a galaxy evolves from a spiral to a ball, not vice versa.

Dr. Shapley crisply offered this rebuttal to Sir James in a lecture at Philadelphia's Franklin Institute, which this week awarded him its famed Franklin Medal for his galactic researches.

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