The Froth of Space

This column, for the most part, is not about what we ordinarily see. Most of then objects talked about can only be seen with a telescope; some only with the largest telescopes we have built. That we can talk about these things at all is a tribute to our imagination.

We start with what we all see: the stars. What often appears to us as a single star is revealed, through a telescope, as a whole stellar system -- many stars circling one another as they move together through space. Sometimes these groups, or clusters, can even be seen by the unaided eye: the Pleiades or the Beehive cluster are like that.

Even the galaxies themselves, each one a vast system of billions of stars, cluster together. A dozen nearby galaxies, including our own Milky Way and our nearest galactic neighbor, the Andromeda galaxy, form together the "Local Group." This group, in turn, is part of a larger cluster of galaxies, the "Virgo Cluster," fifty million light years away in the direction of the star Spica. And finally, in what has been called "the realm of the galaxies," thousands of these galaxies are joined together in the Virgo supercluster.

(To find the stars Spica and Arcturus, start at the Big Dipper. The curve of its tail points to Arcturus -- "arc to Arcturus." Continue this path to Spica -- "speed on to Spica.")

Between these vast superclusters of galaxies -- nothing. Between are the "voids," tremendous regions where there are no galaxies, or only a few. In the direction of the constellation Bootes, south of brilliant Arcturus, is the vast "Bootes Void," a region of space hundreds of millions of light years across containing almost no galaxies at all. Throughout space there is an alternation of superclusters of galaxies and -- nothing.

Space is like a vast froth of soapy foam. Superclusters of galaxies are found on the skin of the bubbles. The bubbles themselves -- the voids -- are nearly empty. What we see as we look through the largest telescopes across billions of light years is the structure of the universe itself. And it is stranger than anyone had ever thought.

(04/09/08)