Astronomical Line Polarization Through Gas Transport

Book chapter, 2026

Magnetic fields are critical to the dynamics of the interstellar medium (ISM), influencing star formation and interstellar gas dynamics. This paper explores a novel way to probe magnetic fields through molecular line polarization mechanism, that is based on the experimentally well-established Senftleben-Beenakker (SB) effect. In molecular line polarization through SB effects, gaseous transport processes such as viscous strain and thermal gradients, cause molecules to align through directional collisions, subsequently polarizing their emission lines. This polarization mechanism differs from the Goldreich-Kylafis (GK) effect, as it is not dependent on optical depth nor non-thermal excitation. We derive a theoretical framework to model molecular alignment due to the SB effect. We discuss the applicability of SB polarization as a tool to trace magnetic fields in turbulent media and accretion disks.