Lady In Red: Andromeda Galaxy Shines In Spitzer's Eyes

Andromeda is the most-studied galaxy outside our own Milky Way, yetSpitzer's sensitive infrared eyes have detected captivating newfeatures, including bright, aging stars and a spiral arc in the centerof the galaxy. The infrared image also reveals an off-centered ring ofstar formation and a hole in the galaxy's spiral disk of arms. Theseasymmetrical features may have been caused by interactions with theseveral satellite galaxies that surround Andromeda.

"Occasionally small satellite galaxies run straight through biggergalaxies," said Dr. Karl Gordon of the Steward Observatory, Universityof Arizona, Tucson, lead investigator of the new observation. "Itappears a little galaxy punched a hole through Andromeda's disk, muchlike a pebble breaks the surface of a pond."

The new false-color Andromeda image is available at http://www.spitzer.caltech.edu/spitzer/ .

Approximately 2.5 million light-years away, Andromeda is the closestspiral galaxy and is the only one visible to the naked eye. Unlike ourMilky Way galaxy, which we view from the inside, Andromeda is studiedfrom the outside. Astronomers believe that Andromeda and the Milky Waywill eventually merge together.

Spitzer detects dust heated by stars in the galaxy. Its multibandimaging photometer's 24-micron detector recorded approximately 11,000separate infrared snapshots over 18 hours to create the newcomprehensive mosaic. This instrument's resolution and sensitivity is avast improvement over previous infrared technologies, enablingscientists to trace the spiral structures within Andromeda to anunprecedented level of detail.

"In contrast to the smooth appearance of Andromeda at opticalwavelengths, the Spitzer image reveals a well-defined nuclear bulge anda system of spiral arms," said Dr. Susan Stolovy, a co-investigatorfrom the Spitzer Science Center at the California Institute ofTechnology, Pasadena.

The galaxy's central bulge glows in the light emitted by warm dustfrom old, giant stars. Just outside the bulge, a system of inner spiralarms can be seen, and outside this, a well-known prominent ring of starformation.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages theSpitzer mission for NASA's Science Mission Directorate, Washington.Science operations are conducted at the Spitzer Science Center at theCalifornia Institute of Technology. The Jet Propulsion Laboratory is adivision of Caltech.