Shining a Light on Cool Pools of Gas in the Galaxy

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Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov

News feature: 2013-199 Jun. 11, 2013

Shining a Light on Cool Pools of Gas in the Galaxy

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.php?release=2013-199&cid=release_2013-199

Newly formed stars shine brightly, practically crying out, "Hey, look at me!" But not
everything in our Milky Way galaxy is easy to see. The bulk of material between the stars
in the galaxy -- the cool hydrogen gas from which stars spring -- is nearly impossible to
find.

A new study from the Hershel Space Observatory, a European Space Agency mission
with important NASA participation, is shining a light on these hidden pools of gas,
revealing their whereabouts and quantities. In the same way that dyes are used to
visualize swirling motions of transparent fluids, the Herschel team has used a new tracer
to map the invisible hydrogen gas.

The discovery reveals that the reservoir of raw material for making stars had been
underestimated before -- almost by one third -- and extends farther out from our galaxy's
center than known before.

"There is an enormous additional reservoir of material available to form new stars that we
couldn't identify before," said Jorge Pineda of NASA's Jet Propulsion Laboratory,
Pasadena, Calif., lead author of a new paper on the findings published in the journal
Astronomy and Astrophysics.

"We had to go to space to solve this mystery because our atmosphere absorbs the specific
radiation we wanted to detect," said William Langer of JPL, principal investigator of the
Herschel project to map the gas. "We also needed to see far-infrared light to pinpoint the
location of the gas. For both these reasons, Herschel was the only telescope for the job."

Stars are created from clouds of gas, made of hydrogen molecules. The first step in
making a star is to squeeze gas together enough that atoms fuse into molecules. The gas
starts out sparse but, through the pull of gravity and sometimes other constricting forces,
it collects and becomes denser. When the hydrogen gets dense enough, nuclear fusion
takes place and a star is born, shining with starlight.

Astronomers studying stars want to follow this journey, from a star's humble beginnings
as a cloud of molecules to a full-blown blazing orb. To do so requires mapping the
distribution of the stellar hydrogen fuel across the galaxy. Unfortunately, most hydrogen
molecules in space are too cold to give off any visible light. They lurk unseen by most
telescopes.

For decades, researchers have turned to a tracer molecule called carbon monoxide, which
goes hand-in-hand with the hydrogen molecules, revealing their location. But this method
has limitations. In regions where the gas is just beginning to pool -- the earliest stage of
cloud formation -- there is no carbon monoxide.

"Ultraviolet light destroys the carbon monoxide," said Langer. "In the space between
stars, where the gas is very thin, there is not enough dust to shield molecules from
destruction by ultraviolet light."

A different tracer -- ionized carbon – does, however, linger in these large but relatively
empty spaces, and can be used to pin down the hydrogen molecules. Researchers have
observed ionized carbon from space before, but Herschel has, for the first time, provided
a dramatically improved geographic map of its location and abundance in the galaxy.

"Thanks to Herschel's incredible sensitivity, we can separate material moving at different
speeds," said Paul Goldsmith, a co-author and the NASA Herschel Project Scientist at
JPL. "We finally can get the whole picture of what's available to make future generations
of stars."

Read a more in-depth story about this research from the European Space Agency at
http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=51909 . The technical
paper is online at http://arxiv.org/abs/1304.7770 .

Herschel is a European Space Agency mission, with science instruments provided by
consortia of European institutes and with important participation by NASA. NASA's
Herschel Project Office is based at NASA's Jet Propulsion Laboratory, Pasadena, Calif.
JPL contributed mission-enabling technology for two of Herschel's three science
instruments. The NASA Herschel Science Center, part of the Infrared Processing and
Analysis Center at the California Institute of Technology in Pasadena, supports the
United States astronomical community. Caltech manages JPL for NASA.

More information is online at http://www.herschel.caltech.edu ,
http://www.nasa.gov/herschel and http://www.esa.int/SPECIALS/Herschel .

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