Causal Model for Relativistic Accretion Flow

Abstract.

Accretion onto compact objects is a prominent astrophysical problem involving dissipative fluid flow in strong gravitational fields. The generic approach for modeling is by the relativistic Navier-Stokes-Fourier equations, which are of non-hyperbolic type. Consequently, fluctuations in the dissipative variables (shear stress and beat flux) propagate at causality violating infinite speeds, and thermodynamic equilibrium states are unstable. This description is problematic in particular for systems that undergo variability on timescales shorter than or comparable to the dissipative relaxation times. To overcome these difficulties we proposed (Peitz & Appl [3]) to model relativistic accretion flows using extended causal fluid theories. Here we review such a theory and the corresponding 3+1 representation appropriate for numerical implementation.