ScienceShot: The Ultraviolet Glow of Newborn Stars

NASA/JPL–California Institute of Technology/Brad Baxley/JILA

Sometimes your own star gets in the way of understanding the birth of others. In particular, astronomers would like to see the Milky Way's star-forming regions emit ultraviolet radiation known as Lyman alpha because it's expected to be both strong and a key diagnostic of conditions in stellar nurseries. Lyman alpha arises from hydrogen at a wavelength of 1216 angstroms (121.6 nanometers), but sunlight with the same wavelength illuminates gas that streams into the solar system from beyond, obscuring the view. Fortunately, in 1977, NASA launched the twin Voyager spacecraft—their paths are shown here—and both are escaping the sun's glow: in mid-November, Voyager 1 was 118.9 times farther from the sun than Earth is; for Voyager 2, the comparable figure was 96.9, still more than twice as far out as Pluto. As astronomers report online today in Science, the Voyager spacecraft have now spied Lyman-alpha emission from star-forming regions in the Milky Way. Because the properties of these nearby nurseries are known, the feat will help astronomers better understand conditions in far-off star-forming galaxies—where, ironically enough, Lyman alpha is easier to detect because the expanding universe redshifts the radiation to longer wavelengths so that sunlight doesn't muck up the view.

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