SIMULATIONS OF RELATIVISTIC EXTRAGALACTIC JETS

We present the first results of axisymmetric jet simulations for both nonrelativistic and relativistic (gamma = 5 and 10) flow speeds, emplo ying a relativistic hydrodynamic code which we have found to be both r obust and efficient. We find the same gross morphology in all cases, b ut the relativistic runs exhibit little instability and less well-defi ned structure internal to the jet: this might explain the difference b etween (relatively slow) BL Lac objects and (faster) QSOs. We find tha t the choice of adiabatic index makes a small but discernible differen ce to the structure of the shocked jet and ambient media. Our code emp loys a solver of the Godunov type, with approximate solution of the lo cal Riemann problems, applied to laboratory frame variables. Lorentz t ransformations provide the rest frame quantities needed for the estima tion of wave speeds, etc. This is applied within the framework of an a daptive mesh refinement algorithm, allowing us to perform high-resolut ion, two-dimensional simulations with modest computing resources.