Andromeda Adrift in Sea of Dust in New NASA Image

IMAGE ADVISORY: 2006-082 June 5, 2006

Andromeda Adrift in Sea of Dust in New NASA Image

The Andromeda galaxy, named for the mythological princess who almost
fell prey to a sea monster, appears tranquil in a new image from NASA's
Spitzer Space Telescope. The mesmerizing infrared mosaic shows red
waves of dust over a blue sea of stars.

"What's really interesting about this view is the contrast between the
galaxy's smooth, flat disk of old stars and its bumpy waves of dust
heated by young stars," said Dr. Pauline Barmby of the
Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass. Barmby
and her colleagues recently observed Andromeda using Spitzer.

To view the picture, visit
http://www.spitzer.caltech.edu/Media/releases/ssc2006-14/ .

Barmby and her team used the Spitzer data to make drastically improved
measurements of Andromeda's infrared brightness. They found that the
galaxy shines with the same amount of energy as about 4 billion suns.
Based on these measurements, the astronomers confirmed that there are
roughly 1 trillion stars in the galaxy. Our Milky Way galaxy is
estimated to house a couple of hundred billion stars.

"This is the first time the stellar population of Andromeda has been
determined using the galaxy's infrared brightness," said Barmby. "It's
reassuring to know our numbers are in agreement with previous estimates
of the mass of the stars based on the stars' motion."

The new false-colored portrait also provides astronomers with the best
look yet at the dust-drenched spiral arms that swirl out of the
galaxy's center, a region hidden by bright starlight in visible-light
images. Dust and gas are the building materials of stars. They are
clumped together throughout the spiral arms, where new stars are
forming.

"The Spitzer data trace with startling clarity the star-forming
material all the way into the inner part of the galaxy," said Dr.
George Helou, deputy director of NASA's Spitzer Science Center at the
California Institute of Technology in Pasadena. "The challenge is to
understand what shapes the distribution of this gas and dust, and what
modulates the star formation at different locations."

Spitzer's infrared array camera captured infrared light emanating from
both older stars (blue) and dust made up of molecules called polycyclic
aromatic hydrocarbons (red). These carbon-containing molecules are
warmed by sunlight and glow at infrared wavelengths. They are often
associated with dense clouds of new stars, and can be found on Earth in
barbecue pits and car exhaust, among other places.

The Andromeda galaxy, also known by astronomers as Messier 31, is
located 2.5 million light-years away in the constellation Andromeda. It
is the closest major galaxy to the Milky Way, making it the ideal
specimen for carefully examining the nature of galaxies. On a clear,
dark night, the galaxy can be spotted with the naked eye as a fuzzy
blob.

Andromeda spans about 260,000 light-years, which means that a light
beam would take 260,000 years to travel from one end of the galaxy to
the other. By comparison, the Milky Way is about 100,000 light-years
across. When viewed from Earth, Andromeda occupies a portion of the sky
equivalent to seven full moons.

Spitzer's wide field of view allowed the telescope to capture a
complete snapshot of the Andromeda galaxy, though the task wasn't easy.
The final mosaic consists of 3,000 or so individual picture frames
stitched together seamlessly.

Barmby presented these observations today at the 208th meeting of the
American Astronomical Society in Calgary, Canada. A previous image of
Andromeda taken with Spitzer's longer-wavelength infrared camera can be
found at
http://www.spitzer.caltech.edu/Media/releases/ssc2005-20/ssc2005-20a.shtml

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

Other members of Barmby's team include: Drs. Steven Willner, Matthew
Ashby, John Huchra and Michael Pahre of the Harvard-Smithsonian Center
for Astrophysics; Drs. Luciana Bianchi and David Thilker of The Johns
Hopkins University, Baltimore, Md.; Drs. Charles Engelbracht, Karl
Gordon, Joannah Hinz, Pablo Pérez-González and George Rieke of the
University of Arizona, Tucson; and Drs. Robert Gehrz, Roberta
Humphreys, Elisha Polomski and Charles Woodward of the University of
Minnesota, Twin Cities.

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. 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.
.

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