Don Savage

Headquarters, Washington, DC

(Phone: 202/358-1547)

Bill Steigerwald

Goddard Space Flight Center, Greenbelt, MD

(Phone: 301/286-5017)



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)

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 195 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
six 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 Dr. 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 Dr. 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 Dr. Warren Moos, 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

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

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 Dr. Michael Shull of the
University of Colorado, and hot gas “winds” from stars so bright
they nearly blow themselves apart, presented by Dr. John Hutchings
of the National Research Council of Canada.

New images related to this science, and more information
about FUSE, can be found on the internet at: