Andrew Yee
July 22nd 05, 02:29 AM
University of Chicago News Office
Chicago, Illinois
Press Contact:
Steve Koppes, (773) 702-8366
June 29, 2005
Scientist refines cosmic clock to determine age of Milky Way
The University of Chicago's Nicolas Dauphas has developed a new way to
calculate the age of the Milky Way that is free of the unvalidated
assumptions that have plagued previous methods. Dauphas' method, which he
reports in the June 29 issue of the journal Nature, can now be used to
tackle other mysteries of the cosmos that have remained unsolved for
decades.
"Age determinations are crucial to a fundamental understanding of the
universe," said Thomas Rauscher, an assistant professor of physics and
astronomy at the University of Basel in Switzerland. "The wide range of
implications is what makes Nicolas' work so exciting and important."
Dauphas, an Assistant Professor in Geophysical Sciences, operates the
Origins Laboratory at the University of Chicago. His wide-ranging
interests include the origins of Earth's atmosphere, the oldest rocks that
may contain evidence for life on Earth and what meteorites reveal about
the formation of the solar system.
In his latest work, Dauphas has honed the accuracy of the cosmic clock by
comparing the decay of two long-lived radioactive elements, uranium-238
and thorium-232. According to Dauphas' new method, the age of the Milky
Way is approximately 14.5 billion years, plus or minus more than 2 billion
years.
That age generally agrees with the estimate of 12.2 billion years --
nearly as old as the universe itself -- as determined by previously
existing methods. Dauphas' finding verifies what was already suspected,
despite the drawbacks of existing methods: "After the big bang, it did not
take much time for large structures to form, including our Milky Way
galaxy," he said.
The age of 12 billion years for the galaxy relied on the characteristics
of two different sets of stars, globular clusters and white dwarfs. But
this estimate depends on assumptions about stellar evolution and nuclear
physics that scientists have yet to substantiate to their complete
satisfaction.
Globular clusters are clusters of stars that exist on the outskirts of a
galaxy. The processes of stellar evolution suggested that most of the
stars in globular clusters are nearly as old as the galaxy itself. When
the big bang occurred 13.7 billion years ago, the only elements in the
universe were hydrogen, helium and a small quantity of lithium. The Milky
Way's globular clusters have to be nearly that old because they contain
mostly hydrogen and helium. Younger stars contain heavier elements that
were recycled from the remains of older stars, which initially forged
these heavier elements in their cores via nuclear fusion.
White dwarf stars, meanwhile, are stars that have used up their fuel and
have advanced to the last stage of their lives. "The white dwarf has no
source of energy, so it just cools down. If you look at its temperature
and you know how fast it cools, then you can approximate the age of the
galaxy, because some of these white dwarfs are about as old as the
galaxy," Dauphas said.
A more direct way to calculate the age of stars and the Milky Way depends
on the accuracy of the uranium/thorium clock. Scientists can
telescopically detect the optical "fingerprints" of the chemical elements.
Using this capability, they have measured the uranium/thorium ratio in a
single old star that resides in the halo of the Milky Way.
IMAGE CAPTION:
[http://www-news.uchicago.edu/releases/05/050629.milkyway.jpg (263KB)]
The University of Chicago's Nicolas Dauphas has estimated the age of the
Milky Way at approximately 14.5 billion years by combining telescopic
observations with laboratory analysis of meteorites, such as the Murchison
meteorite from Australia, pictured here.
Image courtesy of Nicolas Dauphas, University of Chicago
Chicago, Illinois
Press Contact:
Steve Koppes, (773) 702-8366
June 29, 2005
Scientist refines cosmic clock to determine age of Milky Way
The University of Chicago's Nicolas Dauphas has developed a new way to
calculate the age of the Milky Way that is free of the unvalidated
assumptions that have plagued previous methods. Dauphas' method, which he
reports in the June 29 issue of the journal Nature, can now be used to
tackle other mysteries of the cosmos that have remained unsolved for
decades.
"Age determinations are crucial to a fundamental understanding of the
universe," said Thomas Rauscher, an assistant professor of physics and
astronomy at the University of Basel in Switzerland. "The wide range of
implications is what makes Nicolas' work so exciting and important."
Dauphas, an Assistant Professor in Geophysical Sciences, operates the
Origins Laboratory at the University of Chicago. His wide-ranging
interests include the origins of Earth's atmosphere, the oldest rocks that
may contain evidence for life on Earth and what meteorites reveal about
the formation of the solar system.
In his latest work, Dauphas has honed the accuracy of the cosmic clock by
comparing the decay of two long-lived radioactive elements, uranium-238
and thorium-232. According to Dauphas' new method, the age of the Milky
Way is approximately 14.5 billion years, plus or minus more than 2 billion
years.
That age generally agrees with the estimate of 12.2 billion years --
nearly as old as the universe itself -- as determined by previously
existing methods. Dauphas' finding verifies what was already suspected,
despite the drawbacks of existing methods: "After the big bang, it did not
take much time for large structures to form, including our Milky Way
galaxy," he said.
The age of 12 billion years for the galaxy relied on the characteristics
of two different sets of stars, globular clusters and white dwarfs. But
this estimate depends on assumptions about stellar evolution and nuclear
physics that scientists have yet to substantiate to their complete
satisfaction.
Globular clusters are clusters of stars that exist on the outskirts of a
galaxy. The processes of stellar evolution suggested that most of the
stars in globular clusters are nearly as old as the galaxy itself. When
the big bang occurred 13.7 billion years ago, the only elements in the
universe were hydrogen, helium and a small quantity of lithium. The Milky
Way's globular clusters have to be nearly that old because they contain
mostly hydrogen and helium. Younger stars contain heavier elements that
were recycled from the remains of older stars, which initially forged
these heavier elements in their cores via nuclear fusion.
White dwarf stars, meanwhile, are stars that have used up their fuel and
have advanced to the last stage of their lives. "The white dwarf has no
source of energy, so it just cools down. If you look at its temperature
and you know how fast it cools, then you can approximate the age of the
galaxy, because some of these white dwarfs are about as old as the
galaxy," Dauphas said.
A more direct way to calculate the age of stars and the Milky Way depends
on the accuracy of the uranium/thorium clock. Scientists can
telescopically detect the optical "fingerprints" of the chemical elements.
Using this capability, they have measured the uranium/thorium ratio in a
single old star that resides in the halo of the Milky Way.
IMAGE CAPTION:
[http://www-news.uchicago.edu/releases/05/050629.milkyway.jpg (263KB)]
The University of Chicago's Nicolas Dauphas has estimated the age of the
Milky Way at approximately 14.5 billion years by combining telescopic
observations with laboratory analysis of meteorites, such as the Murchison
meteorite from Australia, pictured here.
Image courtesy of Nicolas Dauphas, University of Chicago