Spherically symmetric collapse: Initial configurations

TL;DR

This paper introduces a new method for modeling spherical gravitational collapse by specifying the energy density as a polynomial function, leading to physically consistent models of compact objects like neutron stars.

Contribution

It proposes an alternative approach using polynomial energy density functions and solves the resulting equations numerically, providing models consistent with physical and stability conditions.

Findings

Model satisfies Buchdahl limit

Energy density and pressure meet physical conditions

Compatible with realistic neutron star parameters

Abstract

The initial state of the spherical gravitational collapse in general relativity has been studied with different methods, especially by using {\it a priori} given equations of state that describe the matter as a perfect fluid. We propose an alternative approach, in which the energy density of the perfect fluid is given as a polynomial function of the radial coordinate that is well-behaved everywhere inside the fluid. We then solve the corresponding differential equations, including the Tolman-Oppenheimer-Volkoff equilibrium condition, using a fourth-order Runge-Kutta method and obtain a consistent model with a central perfect-fluid core surrounded by dust. We analyze the Hamiltonian constraint, the mass-to-radius relation, the boundary and physical conditions, and the stability and convergence properties of the numerical solutions. The energy density and pressure of the resulting matter distribution satisfy the standard physical conditions. The model is also consistent with the Buchdahl limit and the speed of sound conditions, even by using realistic values of compact astrophysical objects such as neutron stars.