Spitzer Reveals 'No Organics' Zone Around Pinwheel Galaxy

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE 818-354-5011
http://www.jpl.nasa.gov

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

IMAGE ADVISORY: 2008-138 July 21, 2008

Spitzer Reveals 'No Organics' Zone Around Pinwheel Galaxy

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 .

-end-

To remove yourself from all mailings from NASA Jet Propulsion Laboratory, please go to http://www.kintera.org/TR.asp?a=hqIQIYOFJlJTJ9L&s=isLYK1MFLeKKJ0OLKsE&m=jmKULcMTIhJaE