Candidate magnetic dust structures for star light polarization

• Published in: Monthly notices of the Royal Astronomical Society Vol. 472; no. 1; pp. 55 - 66
• Main Author: Papoular, R.
• Format: Journal Article
• Language: English
• Published: Oxford University Press 21.11.2017
• Subjects: ISM: lines and bands; ISM: magnetic fields – ISM: molecules; astrochemistry – ISM: dust, extinction
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stx1943

Abstract Rotation damping and alignment are discussed as prerequisites for polarization. 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 and (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 ferromagnetism 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.