Thickness of a mildly relativistic collisional shock wave

We consider an imperfect relativistic fluid in which a shock wave develops and we discuss its structure and thickness, taking into account the effects of viscosity and heat conduction in the form of sound absorption. The junction conditions and the nonlinear equations describing the evolution of the shock are derived with the corresponding Newtonian limit discussed in detail. As in the nonrelativistic regime, the thickness is inversely proportional to the discontinuity in the pressure. However, new terms of purely relativistic origin are also present. In particular, for a viscous polytropic gas, it is found that a purely viscous relativistic shock is thicker than its nonrelativistic counterpart, while for pure heat conduction the contrary is true.