NASA Telescope Reveals Nearby Galaxy's Invisible Arms (GALEX)

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.

News Release: 2005-120 July 25, 2005

NASA Telescope Reveals Nearby Galaxy's Invisible Arms

A new image from NASA's Galaxy Evolution Explorer shows
that a galaxy once thought to be rather plain and old is
actually endowed with a gorgeous set of young spiral arms.

The unusual galaxy, called NGC 4625, is a remarkable find
because it is relatively nearby. Until now, astronomers had
thought that this kind of youthful glow in galaxies was a
thing of the past.

"This galaxy is an amazing surprise," said Dr. Armando Gil
de Paz of the Carnegie Observatories, Pasadena, Calif., lead
author of a paper appearing in the July issue of Astrophysical
Journal Letters. "We are practically up-close and personal
with a galaxy undergoing an evolutionary stage that was
thought to occur only at the dawn of the universe, in very
young and faraway galaxies."

The image can be found at
http://www.nasa.gov/centers/jpl/missions/galex.html or
http://www.galex.caltech.edu/ . It offers astronomers their
best look yet at what our Milky Way galaxy might have looked
like in earlier times.

"We do not fully understand how stars were created in our
galaxy," said Dr. Barry Madore of the Carnegie Observatories,
co-author of the new paper. "This nearby galaxy represents
one of our possible histories, in which stars developed
first in the galaxy core and then later in the arms."

Previous visible-light images of NGC 4625 showed only an
oval-shaped ball of light, with very faint hints of a halo
of spiral arms. These arms were finally revealed to the
ultraviolet eyes of the Galaxy Evolution Explorer. Their
intense brightness indicates that the arms are teeming with
hot, newborn stars, which shine primarily with ultraviolet
light.

"The stars in the arms are about one billion years old,
while the stars in the body are about ten times older," said
Gil de Paz.

NGC 4625's spiral arms are very lengthy, extending four
times beyond the size of the core of the galaxy. They
represent the largest ultraviolet galactic disk discovered so
far.

Also of interest in the new Galaxy Evolution Explorer image
is a nearby companion galaxy, which looks very similar to
NGC 4625, yet has no arms. How could this galactic duo have
turned out so differently? Astronomers do not know, but some
theories hold that the presence of the armless galaxy was
required for NGC 4625 to grow a set.

"We know that interactions between galaxies can spur the
creation of stars, but it is not clear why only one galaxy
ended up with arms," said Dr. Chris Martin of the California
Institute of Technology in Pasadena, Calif, principal
investigator for the Galaxy Evolution Explorer.

Previous studies of the gas distribution around the two
galaxies indicate that NGC 4625 might have developed in a
more dynamically stable environment, while the armless
galaxy grew up in a more chaotic and turbulent setting.

Other authors of this paper include: Dr. S. Boissier,
Carnegie Observatories; Dr. R. Swaters, University of
Maryland, College Park; Dr. R. J. Tuffs, Max Planck Institut
fur Kernphysik, Germany; Dr. K. Sheth, Caltech; Dr. R.C.
Kennicutt, University of Arizona, Tucson; Drs. L. Bianchi and
D. Thilker, Johns Hopkins University, Baltimore, Md.

Caltech leads the Galaxy Evolution Explorer mission and is
responsible for science operations and data analysis. NASA's
Jet Propulsion Laboratory, Pasadena, Calif., 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. South Korea and
France are the international partners in the mission.

For images and information about the Galaxy Evolution
Explorer on the Internet, visit

http://www.galex.caltech.edu/ .

-end-