NASA's Galaxy Evolution Explorer is celebrating its fourth year in space
with some of M81's "hottest" stars.
In a new ultraviolet image, the magnificent M81 spiral galaxy is shown at
the center. The orbiting observatory spies the galaxy's "sizzling young
starlets" as wisps of bluish-white swirling around a central golden glow.
The tints of gold at M81's center come from a "senior citizen" population
of smoldering stars.
"This is a spectacular view of M81," says Dr. John Huchra, of the Harvard
Smithsonian Center for Astrophysics, Cambridge, Mass. "When we proposed to
observe this galaxy with GALEX we hoped to see globular clusters, open
clusters, and young stars...this view is everything that we were hoping
for."
The image is one of thousands gathered so far by GALEX, which launched
April 28, 2003. This mission uses ultraviolet wavelengths to measure the
history of star formation 80 percent of the way back to the Big Bang.
The large fluffy bluish-white material to the left of M81 is a neighboring
galaxy called Holmberg IX. This galaxy is practically invisible to the
naked human eye. However, it is illuminated brilliantly in GALEX's wide
ultraviolet eyes. Its ultraviolet colors show that it is actively forming
young stars. The bluish-white fuzz in the space surrounding M81 and
Holmberg IX is new star formation triggered by gravitational interactions
between the two galaxies. Huchra notes that the active star formation in
Holmberg IX is a surprise, and says that more research needs to be done in
light of the new findings from GALEX.
"Some astronomers suspect that the galaxy Holmberg IX is the result of a
galactic interaction between M81 and another neighboring galaxy M82," says
Huchra. "This particular galaxy is especially important because there are
a lot of galaxies like Holmberg IX around our Milky Way galaxy. By
understanding how Holmberg IX came to be, we hope to understand how all
the little galaxies surrounding the Milky Way developed."
"Four years after GALEX's launch, the spacecraft is performing
magnificently. The mission results have been simply amazing as it helps us
to unlock the secrets of galaxies, the building blocks of our universe,"
says Kerry Erickson, GALEX project manager.
M81 and Holberg IX are located approximately 12 million light-years away
in the northern constellation Ursa Major. In addition to leading the GALEX
observations of M81, Huchra and his team also took observations of the
region with NASA's Spitzer and Hubble space telescopes. By combining all
these views of M81, Huchra hopes to gain a better understanding about how
M81 has developed into the spiral galaxy we see today.
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 from South Korea
and France collaborated on this mission.
