Solution generating theorems for perfect fluid spheres

TL;DR

This paper introduces new transformation and solution-generating theorems for perfect fluid spheres in general relativity, enabling systematic classification and construction of solutions, including connections between known models and new solutions.

Contribution

The paper develops systematic transformation and solution-generating theorems for perfect fluid spheres, linking known solutions and creating new models in a structured way.

Findings

New transformation theorems connect existing perfect fluid solutions.

Solution-generating theorems allow deformation of solutions via pressure and density profiles.

Framework facilitates classification and systematic exploration of perfect fluid spheres.

Abstract

The first static spherically symmetric perfect fluid solution with constant density was found by Schwarzschild in 1918. Generically, perfect fluid spheres are interesting because they are first approximations to any attempt at building a realistic model for a general relativistic star. Over the past 90 years a confusing tangle of specific perfect fluid spheres has been discovered, with most of these examples seemingly independent from each other. To bring some order to this collection, we develop several new transformation theorems that map perfect fluid spheres into perfect fluid spheres. These transformation theorems sometimes lead to unexpected connections between previously known perfect fluid spheres, sometimes lead to new previously unknown perfect fluid spheres, and in general can be used to develop a systematic way of classifying the set of all perfect fluid spheres. In addition, we develop new ``solution generating'' theorems for the TOV, whereby any given solution can be ``deformed'' to a new solution. Because these TOV-based theorems work directly in terms of the pressure profile and density profile it is relatively easy to impose regularity conditions at the centre of the fluid sphere.