NASA's Galaxy-Exploring Mission Celebrates Sixth Anniversary

Feature April 28, 2009

NASA's Galaxy-Exploring Mission Celebrates Sixth Anniversary

NASA's Galaxy Evolution Explorer Mission marks its sixth anniversary studying galaxies
beyond our Milky Way through its sensitive ultraviolet telescope, the only such far-
ultraviolet detector in space.

The mission studies the shape, brightness, size and distance of galaxies across 10 billion
years of cosmic history, giving scientists a wealth of data to help us better understand the
origins of the universe. One such object is pictured here, the galaxy NGC598, more
commonly known as M33.

In these side-by-side images of M33, the ultraviolet image on the left was taken by the
Galaxy Evolution Explorer, while the ultraviolet and infrared image on the right is a blend
of the mission's M33 image and another taken by NASA's Spitzer Space Telescope. M33,
one of our closest galactic neighbors, is about 2.9 million light-years away in the
constellation Triangulum, part of what's known as our Local Group of galaxies.

The Galaxy Evolution Explorer has two detectors: one in far-ultraviolet, which reveals
stars younger than about 10 million years old, and another in near-ultraviolet, which
detects stars younger than about 100 million years old. The left ultraviolet image shows a
map of the recent star formation history of M33. The bright blue and white areas are
where star formation has been extremely active over the past few million years. The
patches of yellow and gold are regions where star formation was more active around 100
million years ago.

The ultraviolet image highlights the most massive young stars in M33. These stars burn
their large supply of hydrogen fuel quickly, burning hot and bright while emitting most of
their energy at ultraviolet wavelengths. Compared with low-mass stars like our sun, which
live for billions of years, these massive stars never reach old age, having a lifespan as short
as a few million years.

Together, the Galaxy Evolution Explorer and Spitzer can see a larger range of the full
spectrum of the sky. Spitzer, for example, can detect mid-infrared radiation from dust
that has absorbed young stars' ultraviolet light. That's something the Galaxy Evolution
Explorer cannot see. The combined image on the right shows in amazing detail the
beautiful and complicated interlacing of hot dust and young stars. In some regions of
M33, dust gathers where there is very little far-ultraviolet light, suggesting that the young
stars are obscured or that stars farther away are heating the dust. In some of the outer
regions of the galaxy, just the opposite is true: There are plenty of young stars and very
little dust.

In the combined image, far-ultraviolet light from young stars glimmers blue, near-
ultraviolet light from intermediate age stars glows green, near-infrared light from old stars
burns yellow and orange, and dust rich in organic molecules burns red. The small blue
flecks outside the spiral disk of M33 are most likely distant background galaxies. This
image is a four-band composite that, in addition to the two ultraviolet bands, includes
near infrared as yellow/orange and far infrared as red.

Since its launch from a Pegasus rocket on April 28, 2003, the Galaxy Evolution Explorer
has imaged more than a half-billion objects across two-thirds of the sky. Highlights over
the past six years include detecting star formation in unexpected regions of the universe
and spotting Mira, a fast-moving older star called a red giant. Astronomers say that
studying Mira's gargantuan cosmic tail is helping us learn how stars like our sun die and
ultimately seed new solar systems.

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. South Korea and France are the
mission's international partners.

For information about the Galaxy Evolution Explorer, go to:
http://www.galex.caltech.edu.

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