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CfA Release No.: 06-31
For Release: Friday, December 1, 2006

NEGATIVE VIBES FROM SPACE

Cambridge, MA - Astronomers have discovered the first negatively charged
molecule in space, identifying it from radio signals that were a mystery
until now. While about 130 neutral and 14 positively charged molecules are
known to exist in interstellar space, this is the first negative molecule,
or anion, to be found.

"We've spotted a rare and exotic species, like the white tiger of space,"
said astronomer Michael McCarthy of the Harvard-Smithsonian Center for
Astrophysics (CfA).

By learning more about the rich broth of chemicals found in interstellar
space, astronomers hope to explain how the young Earth converted these
basic ingredients into the essential chemicals for life. This new finding
helps to advance scientists' understanding of the chemistry of the
interstellar medium, and hence the birthplaces of planets.

McCarthy worked with CfA colleagues Carl Gottlieb, Harshal Gupta (also from
the Univ. of Texas), and Patrick Thaddeus to identify the molecular anion
known as C6H-: a linear chain of six carbon atoms with one hydrogen atom at
the end and an "extra" electron. Such molecules were thought to be
extremely rare because ultraviolet light that suffuses space easily knocks
electrons off molecules. The large size of C6H-, larger than most neutral
and all positive molecules known in space, may increase its stability in
the harsh cosmic environment.

"The discovery of C6H- resolves a long-standing enigma in astrochemistry:
the apparent lack of negatively charged molecules in space," stated
Thaddeus.

The team first conducted laboratory experiments to determine exactly what
radio frequencies to use in their search. Then, they used the National
Science Foundation's Robert C. Byrd Green Bank Telescope to hunt for C6H-
in celestial objects. In particular, they targeted locations in which
previous searches had spotted unidentified radio signals at the
appropriate frequencies.

They found C6H- in two very different locations-a shell of gas surrounding
the evolved red giant star IRC +10216 in the constellation Leo, and the
cold molecular cloud TMC-1 in Taurus. The presence of the anion in both
regions shows that the chemical processes that form C6H- are ubiquitous.
It also suggests that other molecular anions are present and will be found
in the near future.

"This finding is dramatic evidence that our understanding of interstellar
chemistry is still quite rudimentary. It also implies that more molecular
anions, perhaps many, may now be found in the laboratory and in space,"
said McCarthy.

This research will appear in the December 1 issue of The Astrophysical
Journal Letters.

Note to editors:

High-resolution photographs of the Green Bank Telescope are available at

http://www.nrao.edu/imagegallery/php/level2a.php?class=Telescopes&subclass=GBT

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for
Astrophysics (CfA) is a joint collaboration between the Smithsonian
Astrophysical Observatory and the Harvard College Observatory. CfA
scientists, organized into six research divisions, study the origin,
evolution and ultimate fate of the universe.