Morphology and dynamics of relativistic jets

We present a comprehensive analysis of the morphology and dynamics of relativistic pressure-matched axisymmetric jets. The numerical simulations have been carried out with a high-resolution shock-capturing hydro-code based on an aprpoximate relativistic Riemann solver derived form the spectral decomposition of the Jacobian matrices of relativistic hydrodynamics. We discuss the dependence of the jet morphology on several parameters paying special attention to the relativistic effects caused by high Lorentz factors and large internal energies of the beam flow. The parameter space of our analysis is spanned by the ratio of the beam and ambient medium rest mass density (#eta#), the beam Mach number (M_b), the beam Lorentz factor (W_b) and the adiabatic index (#gamma#) of the equation of state (assuming an ideal gas). Both the ultrarelativistic regime (W_b#>=#20) and the hypersonic regime (relativistic March number greater than 100) have been studied. Our results show that the enhancement of the effective inertial mass of the beam due to relativistic effects (through the specific enthalpy and the Lorentz factor) makes relativistic jets significantly more stable than Newtonian jets. We find that relativistic jets propagate very efficiently through the ambient medium at speeds, which agree very well with those obtained form an estimate based on a one-dimensional momentum balance. The propagation efficiency of a relativistic jet is an increasing function of the beam flow velocity. The cocoons of relativistic jets are in general less prominent than those of Newtonian jets. For models with #gamma#=5/3 the cocoon is mainly formed by large vortices and has an almost constant thickness along the beam. Jets with #gamma#=4/3 have thinner cocoons with smaller vortices. For jets with high beam internal energies the cocoons reduce to a small lobe near the head of the jet. The cocoon of a highly supersonic jet is extended and overpressured. Its thickness decreases and the mean pressure inside the cocoon increases with increasing beam flow velocity or beam Lorentz factor. (orig.)Available from TIB Hannover: RR 4697(895) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman