Transverse stability of relativistic two-component jets

TL;DR

This study uses relativistic hydrodynamic simulations to analyze the stability of stratified, rotating two-component jets, revealing the development of shear layers, vortices, and Rayleigh-Taylor instabilities, ultimately demonstrating their nonlinear stability.

Contribution

First detailed simulation of relativistic two-component jet stability showing the formation of shear layers and vortices, confirming their nonlinear stability with a heavy outer jet.

Findings

Extended shear flow layer forms due to body and surface mode interactions.

Counterrotating vortices develop at the shear layer.

Heavy outer jet stabilizes the jet against disruptive instabilities.

Abstract

Context: Astrophysical jets from various sources seem to be stratified, with a fast inner jet and a slower outer jet. As it is likely that the launching mechanism for each component is different, their interface will develop differential rotation, while the outer jet radius represents a second interface where disruptions may occur. Aims: We explore the stability of stratified, rotating, relativistic two-component jets, in turn embedded in static interstellar medium. Methods: In a grid-adaptive relativistic hydrodynamic simulation with the AMRVAC code, the non-linear azimuthal stability of two-component relativistic jets is investigated. We simulate until multiple inner jet rotations have been completed. Results: We find evidence for the development of an extended shear flow layer between the two jet components, resulting from the growth of a body mode in the inner jet, Kelvin-Helmholtz surface modes at their original interface, and their nonlinear interaction. Both wave modes are excited by acoustic waves which are reflected between the symmetry axis and the interface of the two jet components. Their interaction induces the growth of near stationary, counterrotating vortices at the outer edge of the shear flow layer. The presence of a heavy external jet allows to slow down their further development, and maintain a collimated flow. At the outer jet boundary, small-scale Rayleigh-Taylor instabilities develop, without disrupting the jet configuration. Conclusion: We demonstrate that the cross-section of two-component relativistic jets, with a heavy, cold outer jet, is non-linearly stable.