The effect of a two-fluid atmosphere on relativistic stars

TL;DR

This paper models the surface behavior of relativistic radiating stars with a two-fluid atmosphere, analyzing how the exterior null fluid influences the star's evolution, luminosity, and collapse dynamics.

Contribution

It introduces an exact solution for a relativistic star with a two-component exterior atmosphere, highlighting the impact of the null fluid's energy density on stellar evolution.

Findings

Null fluid significantly affects the star's pressure and luminosity.

Exterior energy density influences gravitational collapse rate.

Energy conditions are satisfied in the model.

Abstract

We model the physical behaviour at the surface of a relativistic radiating star in the strong gravity limit. The spacetime in the interior is taken to be spherically symmetrical and shear-free. The heat conduction in the interior of the star is governed by the geodesic motion of fluid particles and a nonvanishing radially directed heat flux. The local atmosphere in the exterior region is a two-component system consisting of standard pressureless (null) radiation and an additional null fluid with nonzero pressure and constant energy density. We analyse the generalised junction condition for the matter and gravitational variables on the stellar surface and generate an exact solution. We investigate the effect of the exterior energy density on the temporal evolution of the radiating fluid pressure, luminosty, gravitational redshift and mass flow at the boundary of the star. The influence of the density on the rate of gravitational collapse is also probed and the strong, dominant and weak energy conditions are also tested. We show that the presence of the additional null fluid has a significant effect on the dynamical evolution of the star.