# Relativistic radiating stars with generalised atmospheres.

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## Date

2010

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## Abstract

In this dissertation we construct radiating models for dense compact stars in relativistic
astrophysics. We first utilise the standard Santos (1985) junction condition to
model Euclidean stars. By making use of the heuristic Euclidean condition and a linear
transformation in the gravitational potentials, we generate a particular exact solution
in closed form to the nonlinear stellar boundary condition. Earlier models of spherical
nonadiabatic gravitational collapse are then extended by considering the effect of radial
perturbations in the matter and metric variables, on the evolution of the stellar
fluid and the dynamics of the collapse process. The governing equation describing the
temporal behaviour of the model is solved on the stellar surface. The model becomes
static in the later stages of collapse. The Santos junction condition is then generalised
to describe a radiating star which has a two-fluid atmosphere, consisting of a radiation
field and a string fluid. We show that in the appropriate limit when the string energy
density goes to zero, the standard result is regained. An exact solution to the generalised
boundary condition is found. The generalised boundary condition is extended to
hold in the case when the shear is nonvanishing. We demonstrate that our results can
be used to model the flow of a string fluid in terms of a diffusion transport process.

## Description

Doctor of Philosophy in Applied Mathematics. University of KwaZulu-Natal, Westville 2010.

## Keywords

Astrophysics., Stars., Theses--Applied mathematics.