GALEX observatory captures galaxies galore
Posted: December 11, 2003

The most sensitive and comprehensive ultraviolet image ever taken of the Andromeda Galaxy, our nearest large neighbor galaxy, has been captured by NASA's Galaxy Evolution Explorer. The image is one of several being released to the public as part of the mission's first collection of pictures.

This image is a Galaxy Evolution Explorer observation of the large galaxy in Andromeda, Messier 31. Andromeda is the nearest large galaxy to our own. The image is a mosaic of 10 separate GALEX images taken in September. The color image (with near ultraviolet shown by red and far ultraviolet shown by blue) shows blue regions of young, hot, high mass stars tracing out the spiral arms where star formation is occurring, and the central orange-white "bulge" of old, cooler stars formed long ago. Credit: NASA/JPL/California Institute of Technology
"The Andromeda image gives us a snapshot of the most recent star formation episode," said Dr. Christopher Martin, Galaxy Evolution Explorer principal investigator and an astrophysics professor at the California Institute of Technology in Pasadena, which leads the mission. "By studying this view of the galaxy in the process of forming stars, we can better understand how that fundamental process works, such as where stars form, how fast and why."

The image of Andromeda, the most distant object the naked eye can see, is a mosaic of nine images taken in September and October of 2003. It combines two ultraviolet colors, one near ultraviolet (red) and one far ultraviolet (blue).

The new collection of images also includes views of several nearby galaxies; Stephan's Quintet of Galaxies; an all-sky survey image of the globular star cluster M2; and a deep image of the sky in the constellation Bootes. The Galaxy Evolution Explorer team is also releasing the first batch of scientific data, so the science community can propose additional observations for the mission. These images and data display the power of the Galaxy Evolution Explorer to collect sensitive ultraviolet images of large parts of the sky.

"It's very rewarding and exciting for the team to see the fruits of their labors," said Kerry Erickson, the mission's project manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "Because people are accustomed to seeing objects in visible light, it's amazing to see how different the universe looks in ultraviolet and how much information is revealed to us by those observations."

Scientists are interested in learning more about the Andromeda galaxy, including its brightness, mass, age, and the distribution of young star clusters in its spiral arms. This will provide a tremendous amount of information about the mechanisms of star formation in galaxies, and will help them interpret ultraviolet and infrared observations of other, more distant galaxies.

This image of the dwarf spiral galaxy NGC 247 was taken by Galaxy Evolution Explorer on October 13, 2003, in a single orbit exposure of 1600 seconds. The region that looks like a "hole" in the upper part of the galaxy is a location with a deficit of gas and therefore a lower star formation rate and ultraviolet brightness. Optical images of this galaxy show a bright star on the southern edge. This star is faint and red in the Galaxy Evolution Explorer ultraviolet image, revealing that it is a foreground star in our Milky Way galaxy.
The Galaxy Evolution Explorer launched on April 28, 2003. Its goal is to map the celestial sky in the ultraviolet and determine the history of star formation in the universe over the last 10 billion years. From its orbit high above Earth, the spacecraft will sweep the skies for up to 28 months using state-of-the-art ultraviolet detectors. Looking in the ultraviolet singles out galaxies dominated by young, hot, short-lived stars that give off a great deal energy at that wavelength. These galaxies are actively creating stars, and therefore provide a window into the history and causes of galactic star formation.

In addition to leading the mission, Caltech is also responsible for science operations and data analysis. JPL, a division of Caltech, manages the mission and led the science instrument development. The mission is part of NASA's Explorers Program, managed by the Goddard Space Flight Center, Greenbelt, Md. The mission's international partners are France and South Korea. Caltech manages JPL for NASA.