NSF PR 01-75 - September 26, 2001
Media contacts:
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Amber Jones, NSF
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(703) 292-8070
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aljones@nsf.gov
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Anne Stark, LLNL
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(925) 422-9799
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stark8@llnl.gov
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Program contact:
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Morris Aizenman
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(703) 292-8807
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maizenma@sf.gov
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Search of Galactic Halo Yields a Treasure Trove
of Variable Stars
A project supported by the National Science Foundation
(NSF) to determine the nature of dark matter in the
halo of the Milky Way has yielded a treasure trove
of data on 73 million stars. Many of them are variable
stars, whose brightness varies over time and which
are particularly useful for astronomical research.
The database, created by an international team in
Australia and the United States, has been made available
to astronomers worldwide via the World Wide Web.
The Massive Compact Halo Objects (MACHO) team scrutinized
the Large and Small Magellanic Clouds, two galaxies
which orbit the Milky Way, and the bulge of the Milky
Way in an eight-year search for massive objects such
as planets or brown dwarfs. These objects are believed
to make up much of the dark matter in the region.
They can be detected through gravitational lensing,
in which the light reaching Earth from extragalactic
stars is amplified due to the gravitational force
generated by nearby massive objects.
As a byproduct, the search yielded images and light
curves of 73 million stars. The brightness of many
of these stars varies in a regular pattern, and their
light curves chart the pattern.
"The light curve is a window into the heart of a star,
providing us with information that is not available
in any other way," said Morris Aizenman, a senior
science advisor at NSF. "As these data are analyzed
by the world’s scientific community, they are certain
to reveal some surprises." One type of variable stars,
Cepheid variables, are useful as "meter sticks" for
measuring distances in the universe. The data could
also be useful for studying the interiors of stars
and their evolution and estimating the age of the
universe.
The light amplifications sought by the MACHO scientists
are so rare that, in order to generate useful data,
they examined millions of stars, using the 1.3-meter
Great Melbourne Telescope at Mt. Stromlo Observatory,
Australia. They believe they have found as many as
40 potential candidates for massive objects.
The images, light curves and a catalog of the variable
stars are available for viewing or downloading from
the MACHO project websites at http://www.macho.mcmaster.ca
and http://www.macho.anu.edu.au.
Sophisticated search engines and image analysis tools
assist researchers accessing the data.
"The combination of large databases and computational
tools are speeding scientific discovery in all fields,
and we wanted to expand this capability for astronomers,"
said U.S. team leader Charles Alcock of the University
of Pennsylvania. Alcock started the MACHO project
in 1990 along with Tim Axelrod, formerly of Lawrence
Livermore Lab and now of the Australian National University.
Team members Kem Cook of Livermore and Robyn Allsman
of the Australian National University led the effort
to make the data available.
The MACHO project received support from the NSF-supported
Center for Particle Astrophysics at the University
of California at Berkeley, Santa Barbara and San Diego;
the Department of Energy’s Lawrence Livermore National
Laboratory; and the Australian National University.
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