Older galaxy pair has surprisingly youthful glow (Forwarded)

East Tennessee State University
Johnson City, Tennessee

Contact:
Mark Hancock
Department of Physics, Astronomy, and Geology
East Tennessee State University
(423) 439-5607

Wednesday, January 10, 2007

Older galaxy pair has surprisingly youthful glow

A pair of interacting galaxies might be experiencing the galactic equivalent
of a mid-life crisis. For some reason, the pair, called Arp 82, didn't make
their stars early on as is typical of most galaxies. Instead, they got a
second wind later in life -- about 2 billion years ago -- and started
pumping out waves of new stars as if they were young again.

The new observations are from NASA's Galaxy Evolution Explorer, NASA's
Spitzer Space Telescope and the Southeastern Association for Research in
Astronomy Observatory at Kitt Peak, Ariz.

Arp 82 is an interacting pair of galaxies with a strong bridge and a long
tail. NGC 2535 is the big galaxy and NGC 2536 is its smaller companion. The
disk of the main galaxy looks like an eye, with a bright "pupil" in the
center and oval-shaped "eyelids." Dramatic "beads on a string" features are
visible as chains of evenly spaced star-formation complexes along the
eyelids. These are presumably the result of large-scale gaseous shocks from
a grazing encounter. The colors of this galaxy indicate that the observed
stars are young to intermediate in age, around 2 million to 2 billion years
old, much less than the age of the universe (13.7 billion years).

The pair first burst with new star formation about 2 billion years ago after
swinging by each other. A second close passage more recently resulted in yet
another batch of star formation.

The puzzle is: why didn't Arp 82 form many stars earlier, like most galaxies
of that mass range? Scientifically, it is an oddball and provides a
relatively nearby lab for studying the age of intermediate-mass galaxies.

In more popular terms, think of this as an example of arrested development.
For some reason, it took a kick-in-the-pants to get the stars forming
recently, whereas most other galaxies of that mass range formed their stars
much earlier (between 4 and 8 billion years ago).

A journal article with a detailed analysis of these data has been accepted
by the Astronomical Journal. This research has been sponsored by NASA.

Graphics and additional information about the Galaxy Evolution Explorer is
online at
http://www.nasa.gov/galex/

More information about Spitzer is online at
http://www.spitzer.caltech.edu/spitzer

The California Institute of Technology in Pasadena, Calif., leads the Galaxy
Evolution Explorer mission and is responsible for science operations and
data analysis. NASA's Jet Propulsion Laboratory, also in Pasadena, manages
the mission and built the science instrument. The mission was developed
under NASA's Explorers Program managed by the Goddard Space Flight Center,
Greenbelt, Md. Researchers sponsored by Yonsei University in South Korea and
the Centre National d'Etudes Spatiales (CNES) in France collaborated on this
mission.

JPL manages the Spitzer Space Telescope mission for NASA's Science Mission
Directorate, Washington. Science operations are conducted at the Spitzer
Science Center at Caltech. Caltech manages JPL for NASA.

IMAGE:
http://sscws1.ipac.caltech.edu/Image...name=sig07-002

PHOTO CREDIT: NASA/JPL-Caltech/M. Hancock, B.J. Smith, C. Struck, M.L.
Giroux, P.N. Appleton, V. Charmandaris and W.T. Reach.