Effect of Interacting Rarefaction Waves on Relativistically Hot Jets

TL;DR

This study investigates how interacting rarefaction waves influence the dynamics and structure of relativistically hot jets, revealing cyclic energy conversion and oscillations that affect jet modulation and reconfinement regions.

Contribution

The paper introduces a detailed analysis of nonlinear rarefaction wave interactions in relativistic jets, demonstrating their impact on jet oscillations and structure evolution through simulations.

Findings

Interacting rarefaction waves cause cyclic energy conversion in jets.

Jet oscillation timescale scales with initial pressure ratio as τ ∝ (P_jet,0/P_amb,0)^{1/2}.

Reconfined jet structure size evolves self-similarly as λ ∝ t^{α/2}.

Abstract

The effect of rarefaction acceleration on the propagation dynamics and structure of relativistically hot jets is studied through relativistic hydrodynamic simulations. We emphasize the nonlinear interaction of rarefaction waves excited at the interface between a cylindrical jet and the surrounding medium. From simplified one-dimensional models with radial jet structure, we find that a decrease in the relativistic pressure due to the interacting rarefaction waves in the central zone of the jet transiently yields a more powerful boost of the bulk jet than that expected from single rarefaction acceleration. This leads to a cyclic in-situ energy conversion between thermal and bulk kinetic energies which induces radial oscillating motion of the jet. The oscillation timescale is characterized by the initial pressure ratio of the jet to the ambient medium, and follows a simple scaling relation $\tau_{\rm oscillation} \propto (P_{\rm jet,0}/P_{\rm amb,0})^{1/2}$. It is confirmed from extended two-dimensional simulations that this radial oscillating motion in the one-dimensional system manifests as modulation of the structure of the jet in a more realistic situation where a relativistically hot jet propagates through an ambient medium. It is found that when the ambient medium has a power law pressure distribution, the size of the reconfinement region along the propagation direction of the jet in the modulation structure $\lambda$ evolves according to a self-similar relation $\lambda \propto t^{\alpha/2}$ where $\alpha$ is the power-law index of the pressure distribution.