NOAO/KPNO--NSO,

DEPARTMENT OF ASTRONOMY

AND STEWARD OBSERVATORY

AND NRAO

The University of Arizona

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JOINT COLLOQUIUM

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Dr. Bruce T. Draine

Department of Astrophysical Sciences, Princeton University

"What Aligns Interstellar Grains?"

ABSTRACT: Polarization of starlight was discovered serendipitously 55 years ago, and immediately attributed to aligned dust grains in the interstellar medium. Since then, astrophysicists have been struggling to understand why the larger dust grains are aligned, while the smaller ones are not, and why grains are aligned in some regions, but not others. The quest to understand grain alignment has been a surprising story of important physical processes that were overlooked for decades.

Grain alignment involves thermal fluctuations in the grain solid, rapid rotation, spontaneous magnetization of spinning grains, and torques due to the magnetic field and starlight. We think we now understand why larger grains are aligned, and why the smaller ones are not -- but Nature might have more surprises in store!

• Thursday, January 15, 2004

• at 4:00 p.m.

• in Steward Observatory Lecture Hall-Room N210

• Refreshments at 3:30 p.m. in the Lobby