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UBC-led team confirms age of universe by new method

Hubble image of M4 cluster

Image: NASA

April 25, 2002: An international research team led by scientists at the University of British Columbia today announced a new estimate of the age of the universe that confirms the age of 13-14 billion years previously estimated by an entirely different method.

Prof. Harvey Richer of UBC's Physics and Astronomy Department, the study's principal investigator, discussed the group's research at a Space Science Update held today at NASA headquarters in Washington, D.C.

"The remarkable thing is that our estimate of the age of the universe, based on burned-out stars, agrees very well with the estimate based on the measured expansion rate. The two methods are absolutely unrelated to each other yet they give the same result -- it's amazing," Richer says.

Previous research setting the age of the universe at 13 to 14 billion years was based on the rate of expansion of space, but the universe's birth date is such a fundamental quantity that astronomers have long sought other age-dating techniques to cross-check their conclusions.

Using NASA's Hubble Space Telescope, Richer's group uncovered the oldest burned-out stars in the Milky Way, which are located in a globular star cluster 6,000 light years from Earth in the constellation Scorpius. These extremely dim and old "clockwork stars" give a completely independent reading on the age of the universe.

Hubble photographed the ancient star cluster for a total of eight days between January and April 2001. The data from the 246 images were painstakingly analyzed at UBC by Richer and UBC postdoctoral student James Brewer over a 12-month period to yield the age estimate. The software for this analysis was written by group member Dr. Peter Stetson of the Herzberg Institute of Astrophysics (NRC) in Victoria.

"We measured the brightness and temperatures of white dwarf stars -- the burned-out remnants of the earliest stars which formed in our galaxy. These stars are wonderful cosmic clocks because they get cooler and fainter in a very predictable way. We measured the faintest, coldest stars in the cluster and used [those] data to analyze their age," Richer says. Richer's group reached the estimate of 13-14 billion years by determining that the ancient white dwarf stars photographed by Hubble are 12 to 13 billion years old. Earlier observations show the first stars formed less than one billion years after the universe's birth in the Big Bang, so finding the age of the oldest stars puts astronomers well within reach of calculating the absolute age of the universe.

"This new observation short-circuits getting to the age question, and offers a completely independent way of pinning down that age," Richer says.

This approach has been recognized as more reliable than age-dating the oldest stars still burning by nuclear fusion, which relies on complex models and calculations about how a star burns its nuclear fuel and ages.

"Everything we know about the universe depends on the age we assign it, and because of this work and the expansion research, we have a good idea of that age," Richer says.

The group's work was supported by Canada's Natural Sciences and Engineering Research Council and a Canada Council Killam Fellowship to Richer. The results of the study are to be published in the Astrophysical Journal Letters later this year.

Source: UBC Public Affairs

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