Robustness of the filamentation instability as shock mediator in arbitrarily oriented magnetic field

TL;DR

This paper demonstrates that the filamentation instability, crucial for shock formation in astrophysics, cannot be stabilized by magnetic fields at any angle, ensuring its occurrence in realistic plasma scenarios.

Contribution

It provides an analytical demonstration that the filamentation instability remains unstable at any magnetic field orientation, extending understanding of shock mediation in astrophysical plasmas.

Findings

Filamentation instability cannot be stabilized by magnetic fields at any angle.

The model accounts for relativistic effects and symmetric counter-streaming plasma shells.

Results guarantee the instability's occurrence in realistic cold plasma conditions.

Abstract

The filamentation instability (sometimes also referred to as "Weibel") is a key process in many astrophysical scenario. In the Fireball model for Gamma Ray Bursts, this instability is believed to mediate collisionless shock formation from the collision of two plasma shells. It has been known for long that a flow aligned magnetic field can completely cancel this instability. We show here that in the general case where there is an angle between the field and the flow, the filamentation instability can never be stabilized, regardless of the field strength. The presented model analyzes the stability of two symmetric counter-streaming cold electron/proton plasma shells. Relativistic effects are accounted for, and various exact analytical results are derived. This result guarantees the occurrence of the instability in realistic settings fulfilling the cold approximation.