LONG BEACH, CALIFORNIA—The circular structure in this infrared image from NASA's Spitzer Space Telescope is the largest hot-hydrogen bubble in our Milky Way galaxy. Measuring 300 light-years across, the bubble, known as G52L, is filled with hydrogen gas that is ionized by the energetic radiation of embedded young stars. In the dusty nebulae around the bubble's rim, the formation of new stars is being stimulated. The giant bubble is one of dozens of similar HII regions (HII is ionized hydrogen) first detected with the 110-meter Robert C. Byrd Green Bank Telescope in West Virginia. The Green Bank Telescope HII Region Discovery Survey, the first results of which were presented here on Wednesday at the 221st meeting of the American Astronomical Society, will provide astronomers with a detailed map of the spiral structure of the Milky Way.
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