2 of this paper we present the equations of radiation hydrodynamics in the viscous limit. Section 3 uses those equations to analyze the free-streaming jet model, and we demonstrate the existence of approximate self-similar solutions in the limit that the interaction between the jet and the ambient medium is concentrated in a thin boundary layer. In section 4 we discuss the implications of our model and make comparisons to the two-stream scenario, and in section 5 we conclude and consider the application of the free-streaming jet model to super-Eddington TDEs, GRBs[, and other astronomical sources]{}.

Governing equations
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When changes in fluid quantities over the mean free path of a photon are small, radiation behaves like an effective viscosity and transfers momentum and energy between neighboring fluid elements. The precise form of the viscosity can be determined by investigating the general relativistic Boltzmann equation, which was recently done by @cou14b for the case where Thomson scattering dominates the interactions between the photons and scatterers in the fluid rest frame. In this limit, they found that the relativistic equations of radiation hydrodynamics for a cold gas (gas pressure much less than the gas rest mass density and radiation pressure) are ([see 