Don Savage
Headquarters, Washington, DC                    January 12, 2000
(Phone:  202/358-1547)

Bill Steigerwald
Goddard Space Flight Center, Greenbelt, MD
(Phone:  301/286-5017)

RELEASE:  00-5

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 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 
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 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:  

                     http://fuse.pha.jhu.edu/

                           -end-

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