Spitzer Reveals 'No Organics' Zone Around Pinwheel Galaxy

http://www.jpl.nasa.gov/news/news.cfm?release=2008-138

Spitzer Reveals 'No Organics' Zone Around Pinwheel Galaxy
Jet Propulsion Laboratory
July 21, 2008

The Pinwheel galaxy is gussied up in infrared light in a new picture
from NASA's Spitzer Space Telescope.

The fluffy-looking galaxy, officially named Messier 101, is dominated
by a mishmash of spiral arms. In Spitzer's new view, in which infrared
light is color coded, the galaxy sports a swirling blue center and a
unique, coral-red outer ring.

A new paper appearing July 20 in the Astrophysical Journal explains
why
this outer ring stands out. According to the authors, the red color
highlights a zone where organic molecules called polycyclic aromatic
hydrocarbons, which are present throughout most of the galaxy,
suddenly
disappear.

Polycyclic aromatic hydrocarbons are dusty, carbon-containing
molecules
found in star nurseries, and on Earth in barbeque pits, exhaust pipes
and anywhere combustion reactions take place. Scientists believe this
space dust has the potential to be converted into the stuff of life.

"If you were going look for life in Messier 101, you would not want to
look at its edges," said Karl Gordon of the Space Telescope Science
Institute in Baltimore, Md. "The organics can't survive in these
regions, most likely because of high amounts of harsh radiation." To
view Spitzer's Pinwheel, visit
http://www.nasa.gov/mission_pages/spitzer/multimedia/20080721a.html

The Pinwheel galaxy is located about 27 million light-years away in
the
constellation Ursa Major. It has one of the highest known gradients of
metals (elements heavier than helium) of all nearby galaxies in our
universe. In other words, its concentrations of metals are highest at
its center, and decline rapidly with distance from the center. This is
because stars, which produce metals, are squeezed more tightly into
the
galaxy's central quarters.

Gordon and his team used Spitzer to learn about the galaxy's gradient
of
polycyclic aromatic hydrocarbons. The astronomers found that, like the
metals, the polycyclic aromatic hydrocarbons decrease in concentration
toward the outer portion of the galaxy. But, unlike the metals, these
organic molecules quickly drop off and are no longer detected at the
very outer rim.

"There's a threshold at the rim of this galaxy, where the organic
material is getting destroyed," said Gordon.

The findings also provide a better understanding of the conditions
under
which the very first stars and galaxies arose. In the early universe,
there were not a lot of metals or polycyclic aromatic hydrocarbons
around. The outskirt of the Pinwheel galaxy therefore serves as a
close-up example of what the environment might look like in a distant
galaxy.

In this image, infrared light with a wavelength of 3.6 microns is
colored blue; 8-micron light is green; and 24-micron light is red. All
three of Spitzer instruments were used in the study: the infrared
array
camera, the multiband imaging photometer and the infrared
spectrograph.

Other authors of the paper include Charles Engelbracht, George Rieke,
Karl A. Misselt, J.D. Smith and Robert Kennicutt, Jr. of the
University
of Arizona, Tucson. Smith is also associated with the University of
Toledo, Ohio, and Kennicutt is also associated with the University of
Cambridge, England.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the
Spitzer
Space Telescope mission for NASA's Science Mission Directorate,
Washington. Science operations are conducted at the Spitzer Science
Center at the California Institute of Technology, also in Pasadena.
Caltech manages JPL for NASA. Spitzer's infrared array camera was
built
by NASA's Goddard Space Flight Center, Greenbelt, Md. The instrument's
principal investigator is Giovanni Fazio of the Harvard-Smithsonian
Center for Astrophysics. Spitzer's infrared spectrograph was built by
Cornell University, Ithaca, N.Y. Its development was led by Jim Houck
of
Cornell. The multiband imaging photometer for Spitzer was built by
Ball
Aerospace Corporation, Boulder, Colo., and the University of Arizona,
Tucson. Its principal investigator is George Rieke of the University
of
Arizona.

For more information about Spitzer, visit
http://www.spitzer.caltech.edu/spitzer and http://www.nasa.gov/spitzer.

------------------------------------------------------------------------

Media contact: Whitney Clavin 818-354-4673/818-648-9734
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@xxxxxxxxxxxx

2008-138
.

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