The interior structure of rotating black holes 2. Uncharged black holes

TL;DR

This paper models the interior structure of uncharged rotating black holes, revealing how counter-streaming flows lead to inflation and collapse near the inner horizon, with specific conditions on accretion flow patterns.

Contribution

It provides a conformally stationary, axisymmetric solution for uncharged rotating black holes with collisionless accretion, detailing inflation and collapse dynamics near the inner horizon.

Findings

Counter-streaming causes exponential inflation and collapse.

Inflation stalls at high curvature, leading to spacetime collapse.

Monopole accretion flow is required for the dominant radial solution.

Abstract

(Abridged) A solution is obtained for the interior structure of an uncharged rotating black hole that accretes a collisionless fluid. The solution is conformally stationary, axisymmetric, and conformally separable, possessing a conformal Killing tensor. Hyper-relativistic counter-streaming between collisionless ingoing and outgoing streams drives inflation at (just above) the inner horizon, followed by collapse. As ingoing and outgoing streams approach the inner horizon, they focus into twin narrow beams directed along the ingoing and outgoing principal null directions, regardless of the initial angular motions of the streams. The radial energy-momentum of the counter-streaming beams gravitationally accelerates the streams even faster along the principal directions, leading to exponential growth in the streaming density and pressure, and in the Weyl curvature and mass function. At exponentially large density and curvature, inflation stalls, and the spacetime collapses. As the spacetime collapses, the angular motions of the freely-falling streams grow. When the angular motion has become comparable to the radial motion, which happens when the conformal factor has shrunk to an exponentially tiny scale, conformal separability breaks down, and the solution fails. The condition of conformal separability prescribes the form of the ingoing and outgoing accretion flows incident on the inner horizon. The dominant radial part of the solution holds provided that the densities of ingoing and outgoing streams incident on the inner horizon are uniform, independent of latitude; that is, the accretion flow is "monopole." The sub-dominant angular part of the solution requires a special non-radial pattern of angular motion of streams incident on the inner horizon. The prescribed angular pattern cannot be achieved if the collisionless streams fall freely from outside the horizon.