Stability of Magnetized Spine-Sheath Relativistic Jets

A new general relativistic magnetohydrodynamics (GRMHD) code “RAISHIN” used to simulate jet generation by non-rotating and rotating black holes with a geometrically thin Keplerian disk finds that the jet forms a spine-sheath (two-component) 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 RAISHN code has been used to study the effects of strong magnetic fields and weakly relativistic shear motion, c/2, on the KH instability associated with a relativistic jet (γ = 2.5) spine-sheath interaction. In the simulations sound speeds up to ∼ c/ √ 3 and Alfvén wave speeds up to ∼ 0.56c are considered. Numerical simulation results are compared to theoretical predictions from a new normal mode analysis of the linearized 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.