Numerical and analytical investigations of radio jet stability

The sensitivity of thin and hot adiabatic supersonic jets to the density gradients in ambient media is explored to understand the longevity and stability of the relativistic plasma beams responsible for fueling the extended radio emissions seen around powerful radio galaxies and quasars. High resolution two-dimensional (2-D) and lower numerical simulations of light supersonic hydro-resolution three-dimensional (3-D) dynamic jets (with radii ;During the jet's passage through the ISM, strong axisymmetric vortices form in the backflowing plasma and help generate a strong conical internal shock. The fluid processed through this shock sees a faster spread of the shear layer. Non-linear hydrodynamical instabilities cause the shear layer to degenerate into a complex pattern of asymmetric vortex rings and streamwise vortex tubes; these produce additional internal shocks. At very late times, 2-D jets stall and their leading portions pinch off from the main flows, which form fresh Mach disks. The 3-D jets suffer from helical instabilities and show bifurcations and trifurcations for inclined ISM/ICM interfaces. Lower Mach number jets always have higher growth rates of the instabilities than do higher Mach number jets. These can lead to mixing between the backflowing cocoon with the jet as well as mixing between the shocked ambient plasma and the shocked jet plasma.;Analytical estimates of the propagation speed of the jets within the ISM match the simulations rather well. The effectiveness of the resonance modes in the presence of inviscid shear layer instabilities is discussed analytically. This analysis shows that subsonic instabilities dominate near the jet's axis.