Hybrid Simulations of Supersonic Shear Flows: I) Particle Acceleration

TL;DR

This paper uses 2D hybrid simulations to study how supersonic shear flows generate shocks, magnetic turbulence, and accelerate particles, revealing differences from subsonic flows and implications for astrophysical environments.

Contribution

It introduces detailed hybrid simulation results of supersonic shear flows, highlighting shocklet formation and particle acceleration mechanisms not previously characterized.

Findings

Shocklet formation in supersonic shear flows

Enhanced particle acceleration at higher Mach numbers

Generation of magnetic turbulence in the flow

Abstract

Supersonic flows are ubiquitous in warm and cool media; their dissipation leads to heating, generation of nonthermal particles, and amplification of background magnetic fields. We present 2D hybrid (kinetic ions - fluid electrons) simulations of decaying shear flows across the subsonic-to-supersonic transition, finding that the canonical Kelvin-Helmholtz instability in subsonic cases gives way to the formation of shocklets in supersonic shears, where dissipation is faster and nonthermal particles are produced. We discuss the dependence on the flow Mach number of particle acceleration, the viscosity induced by kinetic effects, and the production of magnetic turbulence. We outline the potential impact of these findings for turbulence in the warm interstellar medium, for molecular clouds, and for accretion disks, leaving to a companion paper the discussion of the effects on the shear of self-generated and pre-existing energetic particles.