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Media Relations
University of California-Berkeley

Media Contacts:

Robert Sanders
(510) 643-6998, (510) 642-3734
rls{at}pa.urel.berkeley.edu
  
Additional Resources:
  
Ben McCall
(510) 642-1047
bjmccall{at}astron.berkeley.edu

FOR IMMEDIATE RELEASE: Friday, April 04, 2003 

Part 1 of 2

Cosmic Chemistry Inside Interstellar Clouds Points to
Galactic Wind

Berkeley -- A bit of Earth-bound chemistry has led
scientists at the University of California, Berkeley, to
conclude that there is an unsuspected wind of low-energy
cosmic ray particles blowing through the galaxy. 

The cosmic rays aren't energetic enough to make headway
against the solar wind to reach Earth, but they appear
to have a big impact on the chemistry within tenuous
clouds of gas between stars, so-called diffuse
interstellar clouds. 

"This implies a new population of cosmic rays not
energetic enough to make it into dense clouds but able
to penetrate and play a major role in diffuse clouds,"
said astrophysicist and chemist Benjamin J. McCall, a
Miller Post-doctoral Fellow in the departments of
chemistry and astronomy at UC Berkeley. 

Unlike dense clouds, which look black and empty because
the dust and gas block the light of stars forming
inside, diffuse clouds are invisible, betrayed only by
the reddening of stars whose light passes through them. 

McCall and his colleagues estimate a low-energy cosmic
ray flux 40 times greater than standard estimates,
which are based on observations of dense clouds. 

The finding, reported in the April 3 issue of the journal
Nature, implies that cosmic rays are a more significant
source of heating and ionization in diffuse interstellar
gas clouds than generally recognized, reviving a theory
proposed some 30 years ago. The greater ionization also
implies more abundant production of complex molecules
than previously thought. 

"It would be a major development if it is true," said
Carl Heiles, a UC Berkeley professor of astronomy who
studies interstellar magnetic fields. "I think it's
plausible, because there are indications of increased
heating in low-density gas." 

McCall's colleagues include Richard J. Saykally, UC
Berkeley professor of chemistry, and a member of his
group, Alex Huneycutt; astronomer Thomas R. Geballe
of the Gemini Observatory in Hawaii; and a team of
physicists based at the CRYRING in Sweden, led by
Mats Larsson of Stockholm University. 

Though McCall's interpretation is not accepted by all
astronomers, the findings clearly point to something
wrong with current understanding of the chemistry
inside the diffuse clouds that dot the galaxy. 

"Interstellar chemistry is very important in that it
helps determine certain properties of the galaxy, in
particular the intensity of the low-energy part of
the cosmic ray spectrum," said Al Glassgold, professor
emeritus of physics at New York University and now
adjunct professor of astronomy at UC Berkeley. "Ben's
straightforward interpretation ... presents all kinds
of problems understanding what's going on with the
diffuse, and more generally, the entire interstellar
medium. It's a result that shakes up what people
thought they had been understanding reasonably well
now for about two decades." 

Despite the cold, rarified gas and dust in diffuse
clouds -- a mere 100-300 particles per cubic
centimeter -- chemical reactions are ongoing, sparked
by the ATP of the cosmos, H3+. A highly reactive
molecule, H3+ is composed of three hydrogen atoms
linked in the form of an equilateral triangle --
three bare protons enveloped in a cloud of two
electrons. H3+ readily donates an "extra" proton to
other atoms or molecules, leaving behind a hydrogen
molecule, H2, the main component of molecular clouds.
The molecule that accepts the proton is then
activated, itching to start another chemical reaction. 

"H3+ acts like a strong acid," McCall said. "It's very
happy to give up one of its protons to any molecule it
runs into." 

The reaction breeds a cascade of other reactions,
producing many types of organic molecules, from the
simple ones like water, carbon monoxide and hydroxyl
radicals (OH) to complex hydrocarbons. 

"H3+ begins this whole sequence of ion-molecule
chemistry that is fundamental for our understanding
of what's going on in diffuse clouds as well as dense
molecular clouds," said UC Berkeley professor and
chair of physics Chris McKee, a theoretical
astrophysicist who models the interior of interstellar
clouds. 

Many people suspect that hydrocarbons interacting on
the surface of dust grains could have given rise to
the organic molecules essential for the origin of
life. 

H3+ was first detected in dense molecular clouds seven
years ago, and its abundance fits fairly well with
the chemistry of other molecules in such clouds.
Astronomers thought H3+ would be undetectable in
diffuse clouds, however. To their astonishment, in
1997, H3+ was detected in diffuse clouds as a slight
dip in a characteristic wavelength of starlight
passing through a cloud. This absorption line is a
telltale sign that photons are exciting vibrations in
H3+ molecules. 

"It was quite surprising to see H3+ at all in a diffuse
cloud -- there was 100 times more H3+ there than we
would expect," McCall said. "It made no sense at all." 

 - Continued -

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