WASHINGTON (Reuters) - The dimmest, most faded old stars, glimpsed by the Hubble Space Telescope (news - web sites), offered confirmation that the universe is just under 14 billion years of age, scientists said on Wednesday.
That is an estimate, scientists at NASA (news - web sites) headquarters told reporters, with an error margin of 500 million years either way.
But because it was calculated by a completely different method than earlier estimates, it offers independent verification that astronomers are on the right track.
"It's almost as if we were saying, you always thought you knew how old you were, but you never had proof," Bruce Margon of the Space Telescope Science Institute explained. "One day, you open a drawer and there's your birth certificate, and you get the same answer. That's a real triumph."
To get this confirmation, astronomers aimed the orbiting Hubble telescope at a globular cluster of stars in the constellation Scorpio, some 7,000 light-years from Earth. A light-year is the distance light travels in a year, about 6 trillion miles (10 trillion km).
Such clusters are thought to be the oldest structures in the universe, coming into being about a billion years after the theoretical big bang.
Within these clusters are scores of so-called white dwarfs, burned-out stars that have spent all the nuclear fuel at their cores and are simply fading slowly into darkness.
"They're about the most boring stars you can think of, they're just cinders cooling off," Margon said. "It's just the glowing ember of a fire that is gradually cooling down at a predictable rate."
That predictable cooling rate is the key to calculating the age of the universe, Margon and other astronomers said. Since they knew how fast these old stars were cooling, they could figure how old they were by how bright they were.
That number turned out to be just under 13 billion years; the astronomers -- led by Harvey Richer of the University of British Columbia in Vancouver, Canada -- added 1 billion years to account for the billion years that they believe had elapsed before the globular cluster formed, and got their universe age estimate.
PREVIOUS ESTIMATES
Previously, scientists had calculated the age of the universe by measuring how fast galaxies were speeding away from each other as the universe grew. Many scientists have long believed that the universe is expanding at a predictable rate, but there was disagreement over just what this rate was.
In 1997, the Hubble telescope gave a precise measurement for the expansion rate, and a reliable age for the universe of around 15 billion years.
This estimate got complicated in recent years when astronomers using Hubble and other observatories encountered a strange force they called dark energy, which was making the universe expand more rapidly.
With dark energy factored into the equation, astronomers put the universe's age at 13 billion to 14 billion years -- in the same cosmic ballpark as the figure reached by tracking the fading out of the oldest stars.
The dimmest, most faded old stars, glimpsed by the Hubble Space Telescope, offered confirmation that the universe is just under 14 billion years of age, scientists said on April 24, 2002. In the top panel, a ground-based observatory snapped panoramic view of the entire cluster, which contains several hundred thousand stars. The box at left indicates the region observed by the Hubble telescope. The Hubble telescope studied a small region of the cluster. A section of that region is seen in the picture at bottom left. A sampling of an even smaller region is shown at bottom right. This region is only about one light-year across. In this smaller region, Hubble pinpointed a number of faint white dwarfs. The blue circles pinpoint the dwarfs. It took nearly eight days of exposure time over a 67-day period to find these extremely faint stars. (Nasa/Reuters)
That is an estimate, scientists at NASA (news - web sites) headquarters told reporters, with an error margin of 500 million years either way.
But because it was calculated by a completely different method than earlier estimates, it offers independent verification that astronomers are on the right track.
"It's almost as if we were saying, you always thought you knew how old you were, but you never had proof," Bruce Margon of the Space Telescope Science Institute explained. "One day, you open a drawer and there's your birth certificate, and you get the same answer. That's a real triumph."
To get this confirmation, astronomers aimed the orbiting Hubble telescope at a globular cluster of stars in the constellation Scorpio, some 7,000 light-years from Earth. A light-year is the distance light travels in a year, about 6 trillion miles (10 trillion km).
Such clusters are thought to be the oldest structures in the universe, coming into being about a billion years after the theoretical big bang.
Within these clusters are scores of so-called white dwarfs, burned-out stars that have spent all the nuclear fuel at their cores and are simply fading slowly into darkness.
"They're about the most boring stars you can think of, they're just cinders cooling off," Margon said. "It's just the glowing ember of a fire that is gradually cooling down at a predictable rate."
That predictable cooling rate is the key to calculating the age of the universe, Margon and other astronomers said. Since they knew how fast these old stars were cooling, they could figure how old they were by how bright they were.
That number turned out to be just under 13 billion years; the astronomers -- led by Harvey Richer of the University of British Columbia in Vancouver, Canada -- added 1 billion years to account for the billion years that they believe had elapsed before the globular cluster formed, and got their universe age estimate.
PREVIOUS ESTIMATES
Previously, scientists had calculated the age of the universe by measuring how fast galaxies were speeding away from each other as the universe grew. Many scientists have long believed that the universe is expanding at a predictable rate, but there was disagreement over just what this rate was.
In 1997, the Hubble telescope gave a precise measurement for the expansion rate, and a reliable age for the universe of around 15 billion years.
This estimate got complicated in recent years when astronomers using Hubble and other observatories encountered a strange force they called dark energy, which was making the universe expand more rapidly.
With dark energy factored into the equation, astronomers put the universe's age at 13 billion to 14 billion years -- in the same cosmic ballpark as the figure reached by tracking the fading out of the oldest stars.

The dimmest, most faded old stars, glimpsed by the Hubble Space Telescope, offered confirmation that the universe is just under 14 billion years of age, scientists said on April 24, 2002. In the top panel, a ground-based observatory snapped panoramic view of the entire cluster, which contains several hundred thousand stars. The box at left indicates the region observed by the Hubble telescope. The Hubble telescope studied a small region of the cluster. A section of that region is seen in the picture at bottom left. A sampling of an even smaller region is shown at bottom right. This region is only about one light-year across. In this smaller region, Hubble pinpointed a number of faint white dwarfs. The blue circles pinpoint the dwarfs. It took nearly eight days of exposure time over a 67-day period to find these extremely faint stars. (Nasa/Reuters)