Reorienting MHD Colliding Flows: A Shock Physics Mechanism for Generating Filaments Normal to Magnetic Fields

TL;DR

This paper uses numerical simulations to show how reoriented oblique shocks in magnetized colliding flows can produce filaments aligned perpendicular to magnetic fields, matching observations in star-forming regions.

Contribution

It introduces a shock physics mechanism for filament formation normal to magnetic fields through reorientation of oblique shocks in colliding flows.

Findings

Reorientation begins with pressure gradients between collision region and ambient medium.

Post-shock filaments reorient from outside-in, from flow-ambient boundary toward collision axis.

Simulated filament structures resemble observed filaments in Taurus, Serpens South, and Orion A.

Abstract

We present numerical simulations of reorienting oblique shocks that form in the collision layer between magnetized colliding flows. Reorientation aligns parsec-scale post-shock filaments normal to the background magnetic field. We find that reorientation begins with pressure gradients between the collision region and the ambient medium. This drives a lateral expansion of post-shock gas, which reorients the growing filament from the outside-in (i.e. from the flow-ambient boundary, toward the colliding flows axis). The final structures of our simulations resemble polarization observations of filaments in Taurus and Serpens South, as well as the integral-shaped filament in Orion A. Given the ubiquity of colliding flows in the interstellar medium, shock reorientation may be relevant to the formation of filaments normal to magnetic fields.