Alignment of irregular grains by radiative torques: efficiency study

Abstract

We study the efficiency of grain alignment by radiative torques (RATs) for an ensemble of irregular grains. The grains are modeled as ensembles of oblate and prolate spheroids, deformed as Gaussian random ellipsoids, and their scattering interactions are solved using numerically exact methods. We define the fraction of the grains that both rotate fast and demonstrate perfect alignment with grain long axes perpendicular to the magnetic field. We demonstrate that for typical interstellar conditions the degree of alignment arising from the RAT mechanism is significantly larger than that arising from the Davis-Greenstein (DG) mechanism based on paramagnetic relaxation. We quantify a factor related to the efficacy of alignment and show that it is related to a $q_{\max }$-factor of analytical model (AMO) of the RAT theory. Our results indicate that the RAT alignment can potentially be sufficiently strong and to explain observations even if grains do not have magnetic inclusions.

14 pages, 11 figures

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• The Mechanical Alignment of Dust (MAD) I: On the spin-up process of fractal grains by a gas-dust drift
• Polarization from Aligned Dust Grains in the $\beta$ Pic Debris Disk
• Is the mm/submm dust polarization a robust tracer of the magnetic field topology in protostellar envelopes? A model exploration
• Synthetic Modelling of Polarized Dust Emission in Intermediate-Mass YSOs: I: Constraining the Role of Iron Inclusions and Inelastic Relaxation on Grain Alignment with ALMA Polarization
• Effect of Dust Rotational Disruption by Radiative Torques and Implications for F-corona decrease revealed by the Parker Solar Probe
• On planet formation around supermassive black holes and the grain disruption barriers by radiative torques
• Modeling extinction and reddening effects by circumstellar dust in the Betelgeuse envelope in the presence of radiative torque disruption
• Grain alignment and dust evolution physics with polarisation (GRADE-POL). I. Dust polarisation modelling for isolated starless cores
• Large Interstellar Polarisation Survey. III. Observational constraints on the structure of grains