Geometry near the inner horizon of a rotating, accreting black hole

TL;DR

This paper introduces a classical, homogeneous model for the near-inner horizon geometry of rotating, accreting black holes, predicting a Kasner-like collapse and analyzing observable effects for infalling observers.

Contribution

It presents a novel homogeneous model with collisionless null fluid sources, connecting the Kerr metric to a self-similar accreting spacetime and predicting a new collapse behavior near the inner horizon.

Findings

Mass inflation is interrupted by Kasner-like collapse.

Model aligns with conformally-separable Kerr-based models.

Null geodesic analysis reveals potential observational signatures.

Abstract

Here we present a novel classical model to describe the near-inner horizon geometry of a rotating, accreting black hole. The model assumes spacetime is homogeneous and is sourced by radial streams of a collisionless, null fluid, and it predicts that the standard Poisson-Israel mass inflation phenomenon will be interrupted by a Kasner-like collapse toward a spacelike singularity. Such a model is shown to be valid at the inner horizon of astrophysically realistic black holes through comparison to the conformally-separable model, which provides a natural connection of the Kerr metric to a self-similar, accreting spacetime. We then analyze the behavior of null geodesics in our model, connecting them to the Kerr metric in order to answer the practical question of what an infalling observer approaching the inner horizon might see.