Galactic Flapping

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Science  14 Apr 2006:
Vol. 312, Issue 5771, pp. 161
DOI: 10.1126/science.312.5771.161b

The Milky Way's flattened disk contains vast reservoirs of hydrogen gas. Near the edges, the disk consists mostly of hydrogen, with few stars. Radio astronomical observations have revealed warping at these edges, as in a dish or saddle. Weinberg and Blitz modeled this warping phenomenon using perturbation theory calculations. Their results attribute the shape to tidal effects induced by motions of the Milky Way's small neighboring galaxies, the Large and Small Magellanic Clouds. As these satellite galaxies move in orbital loops around the Milky Way, they create trailing wakes in the Milky Way's halo of surrounding dark matter. These wakes in turn can cause the outer edges of the Milky Way's lightweight gas disk to bend and flap like a flag in the breeze. The model describes a dynamic disk, which continually changes its shape as the clouds move along their orbits. The authors further suggest that warp observations offer a useful constraint for determining dark matter distributions. — JB

Astrophys. J. 641, L33 (2006).

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