The mechanical alignment of dust (MAD)

Context. Observations of polarized light emerging from aligned dust grains are commonly exploited to probe the magnetic field orientation in astrophysical environments. However, exact physical processes that result a coherent large-scale grain alignment still far being fully constrained. Aims. In this work, we aim investigate impact gas-dust drift on microscopic level, potentially leading mechanical fractal and subsequently polarization. Methods. We scanned wide range parameters aggregates order statistically analyze average behavior distinct ensembles. detail, spin-up efficiencies for individual were determined utilizing Monte Carlo approach simulate collision, scattering, sticking, evaporation gas surface. Furthermore, rotational disruption was taken into account estimate upper limit possible rotation. The analyzed within mathematical framework dynamics identify long-term stable points parameter space. Here, distinguish between cases direction along lines. Finally, net polarization calculated each collection per ensemble. Results. find purely cold neutral medium be sufficient enough drive elongated alignment. most likely configuration is with rotation axis parallel direction. roundish require supersonic velocity, while rod-like can already align subsonic conditions. predict efficiency unity resulting may rapid where become rotationally disrupted by centrifugal forces. Hence, contribution such ensemble drastically reduces. presence field, velocity required reach roughly one magnitude higher compared case. demonstrate considerable fraction stably lines report 0.6–0.9, indicating alone provide conditions observationally structure. highly inefficient when perpendicular. Conclusions. Our results strongly suggest has consideration as an alternative driving mechanism canonical radiative torque theory fails full spectrum available observations.