ScienceShot: The Milky Way's Dark Skeleton

LONG BEACH, CALIFORNIA—A ribbon of cool gas and dust stretches across the bottom half of this image from NASA's Spitzer Space Telescope, creating a snakelike silhouette in the infrared glow of warmer gas beyond. The infrared dark cloud is more than 300 light-years long but just a few light-years thick; it is located between two of our Milky Way's spiral arms, some 10,000 light-years away from the Earth. Thousands of similar structures could lurk in the galaxy, say astronomers who presented the discovery here yesterday at the 221st meeting of the American Astronomical Society. They compare the dark network to a skeleton, defining the Milky Way's structure. This particular "bone" is millions of times more massive than the sun and lies in the central plane of the galaxy's disk. Future observations and computer simulations should reveal the skeleton's origin, which is presently unknown.

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