Clusters of bright blue stars swirl on the spiral arms of galaxy NGC4603, near the center of the Centaurus Cluster, one of the largest collections or "sheets" of galaxies in the universe. The stars' blue light means that they are young. Most stars begin their lives blue, then turn yellow like our sun, then become red when they enter old age.

The fate of our galaxy lies in this direction.

Right now the galaxy NGC4603, about 108 million light-years away, is a favorite of astronomers because it is the most distant known location of objects called "Cepheid variables," pulsating stars whose frequencies are used to measure the expansion rate of the universe. But over the course of cosmic time, this location may be significant for a different reason. The Milky Way is moving toward the Centaurus Cluster at more than a million miles per hour. The fate of our galaxy lies in this direction.

Why should galaxies align themselves into clusters, rather than being scattered around approximately equidistant from each other? Astronomers have recently begun to speculate that at the heart of each galactic cluster lies a Great Attractor, some source of extremely powerful pull. They just don't know what a Great Attractor might be. Because the effect of gravity declines over distance, the level of power necessary to attract entire galaxies across cosmic space seems so enormous as to border on supernatural. There must be something really Great behind a Great Attractor.