Milky Way galaxy has four arms again
A debate has been raging about whether our galaxy has four spiral arms, or two. A 12-year study of massive stars suggests that it has four.
Our galaxy has four spiral arms, not two, says astronomer James Urquhart at the Max Planck Institute for Radio Astronomy in Bonn, Germany. Urquhart is lead author of new research, published today (December 17, 2013) in the Monthly Notices of the Royal Astronomical Society. He and his team conducted a 12-year survey of massive stars in our galaxy, and, Urquhart says, these stars trace out the galaxy’s four spiral arms.
An investigation into the precise structure of the Milky Way has ongoing, perhaps, for as long as we’ve known we live inside a galaxy, one of billions of islands of stars in space. That awareness hasn’t been around as long as you might think, less than a century. We can’t step outside the Milky Way to get perspective. Every picture you’ve ever seen of it has been an artist’s concept.
So … two arms or four for the Milky Way? Images taken by NASA’s Spitzer Space Telescope in 2008 showed two arms. That’s when the current debate began raging.
In Dr. Urquhart’s study, astronomers are attempting to deduce the shape of our Milky Way galaxy by careful observation of its stars and their distances from us. Massive stars are an obvious choice because they shine so brightly.
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http://earthsky.org/space/our-milky-way-does-have-four-arms-astronomers-say
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