Feb. 27, 2008 Imagine looking at a tree through eyeglasses that only allow red light to pass through. The tree is going to look a lot different than how it would look without the glasses. The same goes for a galaxy when astronomers look at it through different types of telescopes.
This new image from NASA’s Swift satellite demonstrates what happens when astronomers look at a galaxy in ultraviolet light rather than the visible light that we see with our eyes. Swift took the image through a series of filters that only let in ultraviolet light. We cannot see ultraviolet light with our eyes, but we can feel its effects: it gives us sunburn if we stay out in the Sun too long on a bright, sunny day.
The Swift ultraviolet image shows the Triangulum Galaxy, so named because it resides in the northern constellation Triangulum. The galaxy is also known as M33, because it’s the 33rd object in a catalog of sky objects that was assembled by French astronomer Charles Messier in the 1700s. The galaxy itself is about half the size of our Milky Way Galaxy, and is located about 2.9 million light-years from Earth. This means that it takes the light from M33 2.9 million years to reach Earth.
The image itself is actually a mosaic of 13 individual pictures that were taken between December 23, 2007 and January 4, 2008. Astronomer Stefan Immler of NASA’s Goddard Space Flight Center used a computer to stitch the individual pictures into a seamless image. "This is the most detailed ultraviolet image of an entire galaxy ever taken," says Immler.
The image clearly shows the spiral structure of M33. New stars are forming inside the spiral arms. These stars are very hot, and give off a lot of ultraviolet light. This light hits nearby clouds of gas, heating them up and causing them to also shine in ultraviolet light.
"The ultraviolet colors of star clusters tell us their ages and compositions," says Swift team member Stephen Holland of NASA Goddard. "With Swift’s high spatial resolution, we can zero in on the clusters themselves and separate out nearby stars and gas clouds. This will enable us to trace the star-forming history of the entire galaxy.”
"The entire galaxy is ablaze with starbirth," adds Immler. "Despite M33’s small size, it has a much higher star-formation rate than our Milky Way Galaxy. All of this starbirth lights up the galaxy in the ultraviolet."
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