Alignment of Irregular Grains by Radiative Torques: Efficiency Study

Abstract

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 quantify a factor related to the efficacy of alignment and show that it is related to a factor of the analytical model of the RAT theory. For the interstellar radiation field, our results indicate that the degree of RAT alignment can reach ∼0.5, which may be sufficient to explain observations even if grains do not have magnetic inclusions.