Electric dipole moments and disalignment of interstellar dust grains

TL;DR

This paper investigates how electric dipole moments influence the disalignment of interstellar dust grains, providing quantitative estimates that suggest disalignment can be rapid unless grains contain superparamagnetic inclusions.

Contribution

It introduces a new disalignment mechanism involving time-varying electric dipole moments and quantifies disalignment timescales for silicate grains.

Findings

Disalignment times are shorter than alignment timescales for most grains.

Superparamagnetic inclusions can prolong grain alignment.

Electric dipole-induced disalignment is significant for grains >0.1 micron.

Abstract

The degree to which interstellar grains align with respect to the interstellar magnetic field depends on disaligning as well as aligning mechanisms. For decades, it was assumed that disalignment was due primarily to the random angular impulses a grain receives when colliding with gas-phase atoms. Recently, a new disalignment mechanism has been considered, which may be very potent for a grain that has a time-varying electric dipole moment and drifts across the magnetic field. We provide quantitative estimates of the disalignment times for silicate grains with size > approximately 0.1 micron. These appear to be shorter than the time-scale for alignment by radiative torques, unless the grains contain superparamagnetic inclusions.