From: Walter Watts (wlwatts@cox.net)
Date: Thu Apr 25 2002 - 11:49:45 MDT
13 billion. 15 billion.
It's old enough to know better!!
Walter
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Universe Found 13 Billion Years Old
04/25/2002 10:49 AM EDT
By PAUL RECER
WASHINGTON (AP) - Astronomers measuring the last flickering heat of dying stars have come up with a new estimate for the age of the universe: about 13 billion years - slightly younger than previous estimates.
The finding gives "very comparable results" to an earlier study that used a different method to conclude the universe burst into existence with the theoretical "Big Bang"
13 billion to 14 billion years ago, experts say.
Harvey B. Richer, an astronomer at the University of British Columbia, said the new age estimate came from images gathered by the Hubble Space Telescope of the faintest dying stars it could find in M4, a star cluster some 7,000 light-years away.
Richer said the fading stars, called white dwarfs, are actually burnt out coals of stars that were once up to eight times the size of the sun. After they exhausted their fuel, the stars collapsed into Earth-sized spheres of cooling embers that eventually will turn cold and wink out of sight.
Earlier studies had established the rate of cooling for these stars, said Richer. By looking at the very faintest and oldest white dwarfs possible, astronomers can use this cooling rate to estimate the age of the universe.
Speaking at a news conference Wednesday, Richer said the dimmest of the white dwarfs are about 12.7 billion years old, plus or minus about half a billion years.
Richer said it is estimated that star formation did not begin until about a billion years after the Big Bang. He said this means his best estimate for age of the universe is "about 13 billion years."
Three years ago, astronomers using another method estimated the age at 13 billion to 14 billion years. That was based on precise measurements of the rate at which galaxies are moving apart, an expansion that started with the Big Bang. They then back-calculated - like running a movie backward - to arrive at the age estimate.
"Our results are in very good agreement" with Richer's estimate, said Wendy L. Freedman, an astronomer at the Carnegie Observatories in Pasadena, Calif., and a leader of the group performing the universe age calculations three years ago.
Bruce Margon, an astronomer at the Space Telescope Science Institute, said both conclusions are based on "a lot of assumptions" but the fact that two independent methods arrived within 10 percent of the same answer is important.
"To find an independent way to measure the age and then get essentially the same answer is a fantastic advance," said Margon. It may not be the final answer for the universe's age, he said, but is "very, very, very close."
To get the new age estimate, the Hubble telescope collected light from M4 for eight days over a 67-day period. Only then did the very faintest of the white dwarfs become visible.
The faintest of the white dwarfs are less than one-billionth the apparent brightness of the dimmest stars visible to the naked eye.
M4 is a globular cluster, thought to be the first group of stars that formed in the Milky Way galaxy, the home galaxy for the sun, early in the history of the universe. There are about 150 globular clusters in the Milky Way; M4 was selected because it is closest to Earth.
The new age estimate for the universe is the latest in a long series of attempts to measure the passage of time since the Big Bang. Edwin Hubble, the famed astronomer who first proved that the universe is uniformly expanding, estimated in 1928 that the universe was 2 billion years old.
Later studies, using the very expansion that Hubble discovered, arrived at an estimate of about 9 billion years for the universe age. This created a paradox for astronomers because some stars were known to be more ancient and it is impossible for stellar bodies to be older than the universe where they formed.
Freedman and others then determined, using proven values for the brightness and distance of certain stars, that the universe throughout its history has not expanded at a constant rate.
--- On the Net: Hubble Images: http://oposite.stsci.edu/pubinfo/pr/2002/10 NASA: http://www.nasa.gov
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