Simulations of Relativistic Extragalactic Jets
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**Session 41 -- Computational Astrophysics II**
*Display presentation, Wednesday, 1, 1994, 9:20-6:30*

## [41.14] Simulations of Relativistic Extragalactic Jets

*P.A. Hughes (U. Michigan), G.C. Duncan (Bowling Green State U.)*
We present results for 2-D, axisymmetric simulations of flows with Lorentz
factors $\sim 5$ -- $10$, typical of values inferred for superluminal BL~Lacs
and QSOs.

The simulations were performed with a numerical hydrodynamic code that admits
relativistic flow speed. We exploit the property that the relativistic Euler
equations for mass, momentum and total energy densities in the laboratory
frame have the same form as the nonrelativistic equations, to solve for
laboratory frame variables using a conventional Godunov-type scheme with
approximate Riemann solver: the HLLE method. The relativistic nature of the
flow is incorporated by performing a Lorentz transformation at every step, at
each cell center or cell boundary where pressure, sound speed or velocity are
required. Determination of the velocity in this manner is a robust algebraic
procedure within which we can ensure that $vP>
We find all the features seen in the many published nonrelativistic
simulations (Mach disk, cocoon, bow shock etc.), but the relativistic flows
exhibit a less pronounced pattern of incident and reflection shocks on axis.
For flows which have propagated to a fixed number of jet radii, the
Kelvin-Helmholtz instability at the contact surface is much less evident in
the high Lorentz factor cases, supporting the contention that relativistic
flows are less prone to such instability. We describe how the morphology of
the cocoon and shocked ambient gas change with increasing Lorentz factor.

This work was supported by NSF grant AST 9120224 and by the Ohio
Supercomputer Center from a Cray Research Software Development Grant.

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