BALTIMORE, MARYLAND--A wiggly pattern in the way galaxies are arrayed has yielded a new recipe for the early universe. Last week, at a meeting here and another in Cambridge, U.K., astronomers working on an ambitious galaxy survey announced that they had seen subtle variations in the distribution of matter at different scales. The discovery provides an independent method of calculating the composition of the cosmos shortly after the big bang.
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Galaxy splotches. The 2dF survey shows a slice of the universe.
CREDIT: ANGLO-AUSTRALIAN OBSERVATORY |
The Two Degree Field (2dF) survey is halfway through its attempt to map 250,000 galaxies. The distribution of those galaxies depends crucially on events in the very early universe. For a few hundred thousand years after the big bang, pressure waves bounced through a seething plasma of matter and energy. As the universe grew and cooled, the compressed regions gave rise to massive clusters of galaxies, while the rarefied ones stayed relatively free of matter. Thus, wiggles in the distribution of galaxies--bumpy features in the graph that describes clumps of matter and voids on various scales--can reveal what the acoustic waves in the early universe were like, as well as the nature of the matter and energy soon after the big bang.
"When you make plots, you do see bumps, hills, and valleys," says Cambridge University astrophysicist Ofer Lahav, a member of the 2dF team. "When we all first saw the pictures, we were very excited." Although Lahav advises caution in interpreting such preliminary results, he says the measurements indicate that baryonic, or ordinary, matter in the early universe weighed in at 5% of the mass needed to give space the shape that cosmologists prefer. That's smack-dab between the 4% predicted by theories of how atomic nuclei were generated in the early universe and the 6% implied by measurements of cosmic background radiation, so it is too early to try to use the 2dF data to resolve which theory needs adjustment.
Even so, wiggles in the graph "would be extremely exciting," says Max Tegmark, a physicist at the University of Pennsylvania in Philadelphia, as they would be an important signature of baryons soon after the big bang. University of Chicago astrophysicist Michael Turner thinks the results are intriguing but reserves judgment for the moment. "We don't have to debate each other until we're blue in the face," he says. "There's more data coming."
--CHARLES SEIFE
Related sites
The Two Degree Field project
The Baltimore meeting's home page
