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Session 16 - Interstellar Grains, PAH's and the Interstellar Bands.
Display session, Monday, January 13
Metropolitan Ballroom,

[16.02] Alignment of Interstellar Grains by Starlight

B. T. Draine (Princeton Univ. Obs.), J. C. Weingartner (Physics Dept., Princeton Univ.)

The alignment of interstellar grains with the Galactic magnetic field has been known for nearly 50 years, but the physical process responsible for this alignment has proved elusive. A new mechanism -- radiative torques due to anisotropic starlight -- will be presented and shown to be a critical part of the grain alignment story. We recently showed that these radiative torques can drive irregular grains to extremely superthermal rotation rates; here we report the effects of these torques on the direction of the grain angular momentum J. While the details depend upon the grain size and shape, and upon the angle \psi between the local magnetic field B_0 and the direction of the starlight anisotropy, we show that for diffuse cloud conditions the starlight torques frequently act to bring the grain angular momentum J into alignment with B_0.

It therefore appears that the longstanding mystery has been solved -- the observed alignment of interstellar grains is due to radiative torques produced by anisotropic starlight!

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Program listing for Monday