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NSF PR 01-06 - January 30, 2001
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Amber Jones
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John Graham
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Southern Star Pulsates Like the Sun, Say Astronomers
Australian telescope measures Beta Hydri's solar-like
oscillations
An international team of astronomers has precisely
measured the oscillations of a sun-like star. The
measurements provide clues to the star's internal
structure that will help scientists test models and
theories of stellar evolution.
Beta Hydri is a nearby star in the constellation Hydrus,
or Southern Water Snake. It is similar to the sun
in mass and temperature, but is estimated to be about
seven billion years old, compared to about 4.5 billion
years for the sun.
"Beta Hydri gives us a good idea of what the sun will
look like in a few billion years," said researcher
Tim Bedding of the University of Sydney. Bedding,
Paul Butler of the Carnegie Institution of Washington
and colleagues from the United States, Australia,
Denmark and Switzerland studied the star with the
3.9 meter Anglo-Australian Telescope at Siding Spring,
Australia. The research is supported by the National
Science Foundation.
By learning about the structure of such stars, scientists
can test theories about the creation, structure and
eventual demise of stars like our sun. These theories
are tested by comparing actual data with predictions
generated by computer models. Today's computers can
simulate billions of years of aging of a star in minutes.
Bedding's and Butler's team precisely measured tiny,
periodic variations, or oscillations, in the velocity
of material moving on or near the surface of the star.
Twelve hundred measurements were taken over five nights
in June 2000. The results will be published in an
upcoming issue of the Astrophysical Journal Letters.
Ever since the discovery in 1979 of tiny oscillations
-with periods of as little as five minutes -- on the
surface of the sun, scientists have looked for the
same minute motions in stars similar to the sun. Since
Beta Hydri is older than the sun, the oscillation
periods were expected to be longer, on the order of
15 to 20 minutes. The astronomers found, indeed, that
the star's oscillation period was 17 minutes.
Just as seismologists use sound waves to probe the
interior of the earth, astronomers use similar techniques
to probe the interior of a star and determine details
such as temperature, rotation and composition. Because
oscillation periods increase as stars get older, these
techniques also allow scientists to estimate the ages
of stars.
"Detecting these seismic waves on Beta Hydri is like
feeling the pulse of the star," said Butler. "Just
as a person's pulse reveals information about the
heart, these oscillations allow us to peer deep into
the center of the star to tell us about conditions
there."
The team used a spectroscopic technique developed by
Butler and Geoff Marcy, of the University of California
at Berkeley, to detect tiny velocity variations in
astronomical objects. Butler, Marcy and other colleagues
have used the technique to find new planets, including
three recently detected with the Anglo Australian
telescope.
Studies of another star, Procyon, have also revealed
evidence of oscillations similar to those of the sun.
However, Bedding's and Butler's team believes the
measurements of Beta Hydri provide the clearest evidence
to date.
Editors: For illustrations see:
http://www.physics.usyd.edu.au/~bedding/mons/visual.html
and
http://www.aao.gov.au/images.html/captions/aat001.html
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