Re: Seeing Double: Spitzer Captures Our Galaxy's Twin

From: William Phillips (wrp_at_dodo.com.au)
Date: 07/03/04 

Date: Sat, 03 Jul 2004 01:52:17 GMT

I what way is this galaxy a "twin" of the milky way?
For example, NGC7331 does NOT have a bar

"Ron" <baalke@earthlink.net> wrote in message
news:d5786437.0406281643.30914593@posting.google.com...
> EDIA RELATIONS OFFICE
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> NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
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> http://www.jpl.nasa.gov
>
> Whitney Clavin (818) 354-4673
> Jet Propulsion Laboratory, Pasadena, Calif.
>
> Image Advisory: 2004-165 June 28, 2004
>
> Seeing Double: Spitzer Captures Our Galaxy's Twin
>
> What would our Milky Way galaxy look like if we could travel outside
> it and snap a picture? It might look a lot like a new image by NASA's
> Spitzer Space Telescope of a spiral galaxy called NGC 7331 - a virtual
> twin of our Milky Way.
>
> The picture, which can be viewed at
> http://photojournal.jpl.nasa.gov/catalog/PIA06322 , shows our twin as
> never before. Its swirling arms spin outward from a central bulge of
> light, which is outlined by a ring of actively forming stars.
>
> "Being inside our galaxy makes it difficult to see what's going on in
> the center," said Dr. J.D. Smith, a member of the team that observed
> NGC 7331, and an astronomer at the University of Arizona, Tucson. "By
> looking at a very similar galaxy, we gain a bird's eye-view of what
> the entire Milky Way might look like."
>
> Such an outside perspective will teach astronomers how our own galaxy,
> as well as others like it, might have formed and evolved.
>
> The latest observations are the first in a large-scale effort to
> observe 75 nearby galaxies with Spitzer's highly sensitive infrared
> eyes. Called Spitzer Infrared Nearby Galaxies Survey, the program will
> combine Spitzer data with that from other ground- and space-based
> telescopes operating at wavelengths ranging from ultraviolet to radio
> to create a comprehensive map of the selected galaxies.
>
> The program's first target, NGC 7331, was chosen in part for its
> striking similarities to the Milky Way. While these so-called twin
> galaxies do not share the same parents, they have many features in
> common, including number of stars, mass, spiral arm pattern and
> star-formation rate of a few stars per year. Whether the Milky Way has
> an inner star-forming ring like that of NGC 7331 is not known. NGC
> 7331 is located about 50 million light-years away in the constellation
> Pegasus.
>
> The new Spitzer image demonstrates the power of the telescope's
> infrared eyes to dissect galaxies into their various parts. Taken by
> the telescope's infrared array camera, the false-colored picture
> readily distinguishes NGC 7331's arms (brownish red), central bulge
> (blue) and star-forming ring (yellow). The composition of materials
> making up these regions was also revealed by the Spitzer observations:
> the central bulge consists primarily of older stars; the ring
> possesses a large amount of gas and dusty organic molecules called
> polycyclic aromatic hydrocarbons, which typically glow when
> illuminated by newborn stars; and the arms contain these same dust
> grains to a lesser degree. Polycyclic aromatic hydrocarbons are also
> found on Earth, on burnt toast and in car exhaust among other places.
>
> Data from Spitzer's infrared spectrograph instrument were also used to
> show that the center of NGC 7331 harbors either an unusually high
> concentration of massive stars, or a moderately active black hole
> about the same size as the one lurking at the core of our galaxy.
>
> These findings will appear in two papers in the September issue of a
> special supplement to the Astrophysical Journal. Dr. Michael W. Regan
> of the Space Telescope Institute, Baltimore, Md., is lead author of a
> paper detailing observations from the infrared array camera, and Smith
> is lead author of a paper on the infrared spectrograph results. The
> Spitzer Infrared Nearby Galaxies Survey project is conducted by a team
> of about 25 scientists from 12 institutions, and is led by principal
> investigator Dr. Robert C. Kennicutt of the University of Arizona,
> Tucson.
>
> Launched August 25, 2003, the Spitzer Space Telescope is the fourth of
> NASA's Great Observatories, a program that also includes the Hubble
> Space Telescope, Chandra X-ray Observatory and Compton Gamma Ray
> Observatory.
>
> JPL manages the Spitzer Space Telescope mission for NASA's Office of
> Space Science, Washington, D.C. Science operations are conducted at
> the Spitzer Science Center at the California Institute of Technology
> in Pasadena. JPL is a division of Caltech. Spitzer's infrared
> spectrograph was built by Cornell University, Ithaca, N.Y., and Ball
> Aerospace Corporation, Boulder, Colo. The instrument's development was
> led by Dr. Jim Houck of Cornell. Spitzer's infrared array camera was
> built by NASA Goddard Space Flight Center, Greenbelt, Md. The camera's
> development was led by Dr. Giovanni Fazio of Smithsonian Astrophysical
> Observatory, Cambridge, Mass.
>
> Additional information about the Spitzer Space Telescope is available
> at http://www.spitzer.caltech.edu .
>
> -end-

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