Collapse and bounce of null fluids

TL;DR

This paper revisits Ori's spacetime surgery proposal to resolve energy condition violations in spherical null fluid collapse, applying it to Husain null fluids and analyzing the resulting matter bounce and discontinuities.

Contribution

It extends Ori's method to more general Husain null fluids, providing a detailed analysis of matter bounces and addressing classification errors in energy condition violations.

Findings

Implementation of spacetime surgery for Husain null fluids

Identification of potential discontinuities and matter shells

Correction of classification errors in Type II stress-energy tensors

Abstract

Exact solutions describing the spherical collapse of null fluids can contain regions which violate the energy conditions. Physically the violations occur when the infalling matter continues to move inwards even when non-gravitational repulsive forces become stronger than gravity. In 1991 Ori proposed a resolution for these violations: spacetime surgery should be used to replace the energy condition violating region with an outgoing solution. The matter bounces. We revisit and implement this proposal for the more general Husain null fluids including a careful study of potential discontinuities and associated matter shells between the regions. Along the way we highlight an error in the standard classification of energy condition violations for Type II stress-energy tensors.