Subsonic Mechanical Alignment of Irregular Grains

TL;DR

This paper demonstrates that irregular grains can be effectively aligned by subsonic gas flows, with alignment efficiency surpassing traditional Gold-type processes, aligning grains perpendicular to magnetic fields.

Contribution

It introduces a new mechanism for grain alignment via subsonic flows, emphasizing the role of grain irregularities and scattering efficiency.

Findings

Alignment is efficient with subsonic flows.

Grains tend to align with long axes perpendicular to magnetic fields.

Helical grains align more effectively than Gold-type processes.

Abstract

We show that grains can be efficiently aligned by interacting with a subsonic gaseous flow. The alignment arises from grains having irregularities that scatter atoms with different efficiency in the right and left directions. The grains tend to align with long axes perpendicular to magnetic field, which corresponds to Davis-Greenstein predictions. Choosing conservative estimates, scattering efficiency of impinging atoms and conservative ``degree of helicity'', the alignment of helical grains is much more efficient than the Gold-type alignment processes.