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The Puzzling Structure of the Universe
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13161 |
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Section : |
NATURAL SCIENCE
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| Issue
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11 / 1987 |
4,203 Words |
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A.K. Finkbeiner
A.K. Finkbeiner is a free-lance writer living in Baltimore. |
Cosmologists ask questions the rest of us quit asking as children: How big is the universe? When did it begin? What else is in it? When will it end?
Some answers have been confirmed by years of observation: The universe is approximately 30 billion light-years in diameter (a light-year is the distance light travels in a year--5,880,000,000,000 miles). It began in an explosion about 15 billion years ago. It could end more than 50 billion years from now, or not at all. Currently, cosmologists are most interested in two fundamental questions: What is the structure of the universe? How did it get that way?
Cosmologists find galaxies, collections of galaxies, and collections of collections of galaxies millions of light-years long. Recently they found one enormous section of the universe that seems to move separately from the rest of it. What is surprising is not the dimensions of the structure, but that the universe has structure at all.
To observe the structure, look at the sky. Most stars seem to be in one part of the sky, along the bright band of the Milky Way. The Milky Way is actually our local galaxy and we sit on its periphery, on one of its spiral arms. We see our galaxy edge-on and up close.
Looking away from the obscuring Milky Way and through a telescope, we see the densest concentration of galaxies in the region around the Andromeda nebula. Again, the reason is that the Milky Way is a member of a cluster of galaxies, called the Local Group, and is on the outskirts of the cluster looking in.
On an even larger scale, more galaxies are in the skies over the Northern Hemisphere than in the skies over the Southern. The reason, once more, is that the Local Group is at the edge of an enormous cluster of clusters of galaxies called the Local Supercluster.
In the 1950s, Gerard de Vaucouleurs of the University of Texas at Austin suggested that perhaps the whole universe is arranged like this, in a vast hierarchy: Maybe everywhere stars gather into galaxies, galaxies into clusters of galaxies, clusters into superclusters.
The Structure
In 1977, James Peebles and his colleagues at Princeton University confirmed de Vaucouleurs' hierarchy by
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