Alignment of Dust by Radiative Torque: Recent Developments
  Alignment of dust by radiative torques (RATs) has proven to be the most
promising mechanism to explain alignment in various astrophysical environments,
from comet atmospheres to accretion disks, molecular clouds, and diffuse
interstellar gas. We discuss some of the major advances, which include, first
of all, formulating of the analytical model of RATs. This model was shown to
reproduce well the torques acting on actual irregular dust grains and allowed
studies of the parameter space for which the alignment happens with long axes
perpendicular and parallel to the magnetic field. Such a study resulted in an
important conclusion that, without any paramagnetic relaxation, the RAT
alignment always happens for interstellar grains with long axes perpendicular
to the magnetic field. We show that the gaseous bombardment in some cases
increases the degree of alignment by knocking out grains from the positions of
imperfect alignment when the grains rotate slowly to more stable positions of
perfect alignment where grains rotate fast. In terms of pinwheel torques,
important revisions have been made in the Lazarian and Draine model of grain
flipping and thermal trapping. Those, however, do not change the major
conclusion that very small grains (i.e. grain size smaller than ~0.03 micron)
should be marginally aligned. Recent work made the RAT alignment a predictive
theory which is ready for quantitative modeling of astrophysical polarization.
We predict that the microwave emission from the Zodiacal dust presents an
important contaminant, which should be included into foreground polarization
templates.
