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History age of the oldest stars in the Galaxy |
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The map of the Milky Way is being redrawn, following the discovery of another arm of the galaxy.The structureconsists of an arc of hydrogen gas 77,000 light years long and a few thousand light years thick running along thegalaxy's outermost edge."We see it over a huge area of sky," says Naomi McClure-Griffiths of the Australia National Telescope Facility in Epping, New South Wales, who led the team that made the discovery.Astronomers are shocked that the feature has been overlooked until now. "I was absolutely flabbergasted, it was quite clearly seen in some of the previous surveys but it was never pointed out or given a name," says Tom Dame at theHarvardSmithsonian Center for Astrophysics in Cambridge, Massachusetts. |
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| Explanation: Is our Galaxy this thin? We believe so. The Milky Way, like NGC 891 pictured above, has the width of a typical spiral galaxy. Spirals have most of their bright stars, gas, and obscuring dust in a thin disk. This disk can be so thin the spiral galaxy appears edge-on like a compact disk seen sideways. The dark band across the middle is a lane of dust which absorbs light. Some of the billions of stars that orbit the center of NGC 891, however, appear to be moving too fast to just be traveling in circles. What causes this peculiar motion? One hypothesis is that NGC 891 has a large bar across its center - a bar that would be obvious were we to see this galaxy face-on instead of edge-on. This false color picture was constructed from 3 near infrared images |
