GRMHD/RMHD Simulations and Stability of Magnetized Spine-Sheath Relativistic Jets

TL;DR

This paper presents GRMHD/RMHD simulations of relativistic jets, revealing how magnetic fields and sheath motion influence jet stability and structure, especially the spine-sheath configuration and Kelvin-Helmholtz instability.

Contribution

It introduces the RAISHIN code for simulating relativistic jets and analyzes the effects of magnetic fields and sheath velocities on jet stability and structure.

Findings

Spine-sheath structure develops in rotating black hole jets.

Strong magnetic fields and sheath speeds affect Kelvin-Helmholtz instability.

Weakly magnetized systems show increased stability with sheath motion.

Abstract

A new general relativistic magnetohydrodynamics (GRMHD) code ``RAISHIN'' used to simulate jet generation by rotating and non-rotating black holes with a geometrically thin Keplarian accretion disk finds that the jet develops a spine-sheath structure in the rotating black hole case. Spine-sheath structure and strong magnetic fields significantly modify the Kelvin-Helmholtz (KH) velocity shear driven instability. The RAISHIN code has been used in its relativistic magnetohydrodynamic (RMHD) configuration to study the effects of strong magnetic fields and weakly relativistic sheath motion, c/2, on the KH instability associated with a relativistic, Lorentz factor equal 2.5, jet spine-sheath interaction. In the simulations sound speeds up to c/1.7 and Alfven wave speeds up to 0.56 c are considered. Numerical simulation results are compared to theoretical predictions from a new normal mode analysis of the RMHD equations. Increased stability of a weakly magnetized system resulting from c/2 sheath speeds and stabilization of a strongly magnetized system resulting from c/2 sheath speeds is found.