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Milky Way map reveals surprises
Aug. 22, 2005
By Terry Devitt, University of Wisconsin
and World Science staff
Our Milky Way galaxy looks quite different from an ordinary spiral galaxy, astronomers
say, after conducting what they call the most comprehensive
structural analysis ever done of the galaxy.
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The Milky Way is no ordinary spiral
galaxy, astronomers say. According to a massive new survey of stars at the heart of the galaxy, the Milky Way has a definitive bar feature -- some 27,000 light years
long -- that distinguishes it from ordinary spiral galaxies, as shown in this artist's rendering.
The small yellow arrow points to our Sun. The
survey sampled around 30 million stars to build a portrait of the
galaxy's inner regions. (Credit: NASA/JPL-Caltech/R. Hurt [SSC/Caltech])
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The survey gives fine details of a long, central bar feature that astronomers
say distinguishes the Milky Way from more usual spiral galaxies.
“This is the best evidence ever for this long central bar in our galaxy,” said Ed Churchwell,
a University of Wisconsin-Madison astronomer and senior author of a paper describing the new work.
The report is to appear in an upcoming edition of
Astrophysical Journal Letters, a research journal.
Using NASA’s orbiting Spitzer Space Telescope, astronomers surveyed some 30 million stars in the plane of the galaxy in an effort to build a detailed portrait of the inner regions of the Milky Way.
The task, Churchwell said, is like trying to describe the boundaries of a forest from a vantage point deep within the woods: “This is hard to do from within the galaxy.”
Spitzer’s capabilities, however, helped the astronomers cut through obscuring clouds of interstellar dust
by gathering infrared light, a type of light which penetrates these clouds. This
provided information on tens of millions of stars at the center of the galaxy.
The new survey gives the most detailed picture to date of the inner regions of the Milky
Way, according to the astronomers. “We’re bringing tens of millions of objects into the equation,” said Robert Benjamin, lead author of the new study and a
physicist at the University of Wisconsin-Whitewater.
The possibility that the Milky Way Galaxy has a long stellar bar through its center has long been considered by astronomers, and such phenomena are not unheard of in galactic taxonomy. They are clearly evident in other galaxies, and it is a structural characteristic that adds definition beyond the swirling arms of typical spiral galaxies.
The new study provides estimates for the size and orientation of the bar that are far different from previous estimates. It shows a bar, consisting of relatively old and red stars, spanning the center of the galaxy roughly 27,000 light years in length.
This is 7,000 light years longer than previously believed, the researchers
said.
The analysis also suggests the bar is oriented at about a 45-degree angle relative to a line joining the sun and the center of the
galaxy, according to the astronomers.
Astronomers have debated whether a presumed central feature of the galaxy would be a bar structure or a central ellipse—or both. The new research, the Wisconsin astronomers said, clearly shows a bar-like structure.
“To date, this is the best evidence for a long bar in our galaxy,” Benjamin
said. “It’s hard to argue with this data.”
The Spitzer Space Telescope went into orbit in August, 2003. NASA’s Jet Propulsion Laboratory in Pasadena, Calif., manages the
telescope.
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