Candidate dust structures for starlight polarization

TL;DR

This paper derives a detailed mathematical model for dust particle rotation damping in magnetic fields, identifying conditions for effective alignment relevant to starlight polarization.

Contribution

It introduces a first-principles expression for damping time and defines conditions for particle alignment, expanding potential candidate dust structures for polarization studies.

Findings

Derived a damping time expression from first principles.

Identified necessary conditions for effective Faraday braking.

Highlighted potential magnetic properties of dust candidates.

Abstract

Rotation damping and alignment are discussed as prerequisites for polarization power. An expression is derived from first principles, for the damping time of the rotation of a particle in a magnetic field, under the Faraday braking torque, provided its electrical properties are known. This makes it possible to describe mathematically, in great detail, the motion of the particle and determine its ultimate state of motion, if a steady state is possible at all. This work defines, first, the necessary condition for the Faraday braking to be effective: a) the net electronic charge distribution should not be uniform throughout; b) the number of vibration modes should exceed a few tens. Resonance of rotation frequency with any of these modes is not a requirement. For alignment to be possible, the ratio of gyroscopic and conservative magnetic to non-conservative (retarding) magnetic torques must be low. Either dia-, para- or ferro-magnetism can do, and a small susceptibility is enough and even preferable. This opens up a wide spectrum of possible candidates. A few examples are given.