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Narrowing the gap between cosmic ages.

Everyone knows you can't be older than your mother. Yet that's the paradox facing cosmologists as they try to determine the age of the universe. On the one hand, astronomers have estimated that globular clusters, the oldest groupings of stars in the universe, have a minimum age of 14 billion years. On the other hand, several determinations of the Hubble constant, which measures the cosmic rate of expansion, indicate that the universe is only 8 to 12 billion years old.

A new analysis of the ages of the 17 oldest clusters in our galaxy lessens the discrepancy. Brian Chaboyer of the Canadian Institute for Theoretical Astrophysics in Toronto and his colleagues fed recent observational data and predictions into more than 4 million computer models of stellar evolution. The team tested how uncertainties in the estimated composition of stars and the rate at which they burn hydrogen would affect the calculated age of clusters.

In the Feb. 16 Science, Chaboyer's team reports that globular clusters have a minimum age of 12 billion years. The new lower limit, at least 2 billion years younger than previous estimates, overlaps-just barely-with some Hubble Space Telescope measurements of the age of the universe. "We're at a point now that a few billion years [less] does start to make a difference," notes Chaboyer.

He adds, however, that a discrepancy remains because "the odds are 20 to 1 that globular clusters are older than 12 billion years."
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Title Annotation:Astronomy; globular clusters older than estimated age of universe
Publication:Science News
Article Type:Brief Article
Date:Feb 24, 1996
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