February 26, 1998 CfA Colloquium


Title: Why are Interstellar Dust Grains Aligned?

Speaker: Bruce Draine

Abstract: The alignment of interstellar grains with the Galactic magnetic field has been known for nearly 50 years, but the explanation for this alignment has been frustratingly elusive. Two pieces of previously-overlooked physics have been added to the discussion: 1) The important effects which thermal fluctuations within the grain have during a so-called "crossover", the period when the grain angular velocity goes through a minimum, and 2) the effects of the external torque due to anisotropic starlight acting on an asymmetric grain. The starlight torque can both spin the grain up to suprathermal rotation rates AND can act systematically to bring the spinning grain into alignment with the magnetic field! With these effects added to the picture, we can now claim to understand why interstellar grains are aligned! Our current understanding of grain alignment will be summarized, with emphasis on both successes and remaining problems.

Reference for students: Draine and Weingartner 1997, ApJ 480, 633.