The role of magnetic field for stability in relativistic jets

Relativistic jets have been observed or postulated in various astrophysical sources, including active galactic nuclei, microquasars in the galaxy and gamma-ray bursts. There are many unsolved problems related to the relativistic jets, for example, formation & acceelration, collimation, and long-term stability. The most promising mechanisms for producing and accelerating relativistic jets, and maintaining collimated structure of relativistic jets involve magnetohydrodynamical (MHD) processes. I have investigated the role of magnetic field for stability of relativistic jets via 3D relativistic MHD simulations. First I have investigated the stability of magnetized spine-sheath (two-component) relativistic jets against Kelvin-Helmholtz (KH) instability. I found that destructive KH modes can be stabilized even when the jet Lorentz factor significantly exceeds the Alfven Lorentz factor. Even in the absence of stabilization, spatial growth of destructive KH modes can be reduced by the presence of mildly relativistic sheath flow around a relativistic jet spine. Second I have studied the temporal and spatial developments of current-driven (CD) kink instability in magnetically dominated relativistic jets. In this investigation, I have considered magnetized, rotating relativistic jets with a force-free helical magnetic field in order to study the influence of the initial configuration on the linear and nonlinear evolution of the instability. The result showed the propagation of a helically kinked structure along the jet and relatively stable configuration for the lighter jets. I identified regions of high current density in filamentary current sheets, indicative of magnetic reconnection, which are associated to the kink unstable regions. I also briefly present results related recollimation shock in magnetized relativistic jets.