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 This is a list of globular clusters. The apparent magnitude does not include an extinction correction. Milky Way These are globular clusters within the halo of the Milky Way galaxy. The diameter is in minutes of arc as seen from Earth. , 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 Noun 1. Hubble constant - (cosmology) the ratio of the speed of recession of a galaxy (due to the expansion of the universe) to its distance from the observer; the Hubble constant is not actually a constant, but is regarded as measuring the expansion rate today , 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 Makeup CITA has a small number of long-term faculty members, and a larger number of short term (3- or 5-year) postdoctoral positions, as well as an active visitor program; the purpose of the relatively high influx of new researchers or visitors is to ensure that timely topics in Toronto and his colleagues fed recent observational data and predictions into more than 4 million computer models of stellar evolution stellar evolution, life history of a star, beginning with its condensation out of the interstellar gas (see interstellar matter) and ending, sometimes catastrophically, when the star has exhausted its nuclear fuel or can no longer adjust itself to a stable . 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 Hubble Space Telescope (HST), the first large optical orbiting observatory. Built from 1978 to 1990 at a cost of $1.5 billion, the HST (named for astronomer E. P. Hubble) was expected to provide the clearest view yet obtained of the universe. 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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