Benjamin and colleagues used Spitzer to make a mosaic of 800,000 images spanning 130 degrees across the sky and one degree above and below the galaxy's mid-plane. It encompassed more than 110 million stars. Using newly developed software to measure star densities, the researchers found the Sagittarius and Norma arms were severely lacking. Scutum-Centaurus was rich enough and Perseus, which wraps around the outer portion of the galaxy, was hidden from view. At a press conference, Benjamin said the two major arms seem to connect up nicely with the near and far ends of the galaxy's central bar. "We can fit the arms together with the bar, like pieces of a puzzle," he said. The two minor arms, Sagittarius and Norma, are believed to be filled with gas and pockets of young stars, while the big arms are dense with both young hot stars and older cooler red giant stars. Our solar system is located near a small spur between Sagittarius and Perseus called the Orion arm, but it may not have started off there. After traveling around the galaxy for the past 4 billion years or so since its formation, the sun may have once resided in a different arm, Benjamin noted. Related Links: |
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