Session CB - Field Theory; Astronomy and Astrophysics; Life on Mars.
MIXED session, Friday morning, November 15
Henry Oliver F, Holiday Inn
Three-dimensional numerical simulations of light supersonic hydrodynamic jets are performed to quantify the crucials role of the interstellar medium (ISM) and intracluster medium (ICM) in defining the gross morphologies of powerful radio galaxies. These jets emerge through power-law atmospheres of their host galaxies and then cross into a hotter, but less dense, ICM. Initially near the orifice, strong axisymmetric vortices form in the backflow plasma and generate a strong first conical internal shock. The fluid processed through this shock sees a faster spread of the shear layer, which destabilizes the flow through a complex pattern of internal shocks, thanks to the presence of non-linear interactive hydrodynamical instabilities. For low Mach number jets, the spread of the sheared flow eventually allows a mixing of the backflow plasma with the forward moving plasma and thus the jet decelerates. The growth of Rayleigh-Taylor instabilities along the contact discontinuity between the shocked ambient plasma and the shocked jet's plasma triggers the entrainment of heavier external gas into the jets. The analytical estimates of the propagation speed of the jets within the ISM match rather well with a model which allows the expansion of the effective Mach disk in power-law ISM profiles. Broader morphologies result when non-zero initial opening angles are employed. An analytical model of the formation of internal shocks is discussed.