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News Release
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January 12, 2000
FOR IMMEDIATE RELEASE
MEDIA CONTACT:
Michael Purdy
mcp@jhu.edu
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FUSE Spacecraft Observes Interstellar
Lifeblood of Galaxies
The extended halo of half-million-degree gas that surrounds the
Milky Way
was generated by thousands of exploding stars, or supernovae, as
our
galaxy evolved, according to new observations by NASA's
Far Ultraviolet
Spectroscopic Explorer (FUSE) spacecraft.
The spacecraft has nearly completed its shakedown phase, and its
first
results are already providing a wealth of new information to
astronomers
about the material that becomes stars, planets, and ourselves.
The new findings confirming the nature of the Milky Way halo are
being
presented today in Atlanta at the 195th meeting of the American
Astronomical Society (AAS).
The roughly football-shaped hot gas halo which surrounds our
galaxy extends
about 5,000-10,000 light years above and below the galactic plane
and thins with distance. One light year is almost 6 trillion
miles.
"The hot gas halo has been known for some time, but we weren't
sure how it
got there or stayed hot," said FUSE co-investigator Blair Savage
of the
University of Wisconsin in Madison. "The new FUSE observations
reveal an
extensive amount of oxygen VI (oxygen atoms that have had five
of their
eight surrounding electrons stripped away) in the halo. Some
scientists
thought that ultraviolet radiation from hot stars could produce
the halo,
but the only way to make the observed amount of oxygen VI is
through
collision with the blast waves from exploding stars, called
supernovae."
"Stars destined to explode don't live long, compared to stars
like our Sun,
so star explosions are actually a record of star formation,"
said George
Sonneborn, FUSE project scientist at NASA's Goddard Space Flight
Center,
Greenbelt, Md. "By comparing supernova generated halos among
galaxies, we
may be able to compare their star formation histories."
"FUSE measures the pulse of the lifeblood of our galaxy, the thin
gas
between stars," said
Warren Moos (pictured at right), FUSE principal
investigator at Johns
Hopkins University in Baltimore. "This interstellar gas courses
through
our veins, because dense clouds of it collapsed to form new
stars and
planets, including our solar system."
The FUSE observatory is now "open for business," Moos said.
"After an
extended on-orbit checkout and debugging period, common for
complex space
observatories, we are now performing observations on a routine
basis for
both members of the Principal Investigator Team and the 62 guest
investigators from around the world selected by NASA for the
first year of
operations.
"We are continuing to tune the instrument," Moos added. "In the
spring we
expect to begin a comprehensive study of the abundance of
deuterium, a
fossil atom left over from the Big Bang. As our team becomes
more
practiced, we need less time to optimize the instrument, and the
amount of
time we can spend on scientific observations will go up. This
means higher
scientific productivity."
FUSE is able to detect interstellar gas and determine its
composition,
velocity and distance by viewing bright celestial objects further
away. The
intervening gas selectively absorbs the light from these objects
in a
unique pattern of colors, depending on the composition of the
gas. The
spectrograph on FUSE separates the light into its component
colors,
similar to the way a prism separates white light into a rainbow.
The
resulting patterns identify the gas like optical fingerprints.
When the
patterns shift to different colors, velocity and distance
measurements can
be inferred.
The FUSE spectrograph is at least 100 times more powerful than
previous
instruments, helping it reveal a large number of new atomic and
molecular
features in interstellar gas that could only be guessed at
before. The
ultraviolet light analyzed by FUSE is invisible to the human
eye.
FUSE scientists are also reporting early results at the AAS
meeting about
investigations into two other components of the galactic
"circulatory
system:" cold clouds of molecular hydrogen where new stars are
born,
presented by Michael Shull of the University of Colorado, and hot
gas
"winds" from stars so bright they nearly blow themselves apart,
presented
by John Hutchings of the National Research Council of Canada.
Editor's Note: New images related to this
science, and more information about FUSE, can be found on the
internet at:
http://fuse.pha.jhu.edu/.
Johns Hopkins University news releases can be found on the
World Wide Web at
http://www.jhu.edu/news_info/news/
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same address.
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