Collapsing shells, critical phenomena and black hole formation

TL;DR

This paper investigates the complex dynamics of gravitational collapse in a two-shell system, revealing rich behaviors including prompt black hole formation, oscillations, and critical phenomena influenced by shell crossings.

Contribution

It introduces a detailed analysis of two-shell gravitational collapse, uncovering critical phenomena and behaviors akin to turbulent dynamics in confined scalar fields.

Findings

Black hole formation depends on shell crossing number

Critical behavior with mass-gap observed at transition points

Rich dynamics including oscillations and prompt collapse

Abstract

We study the gravitational collapse of two thin shells of matter, in asymptotically flat spacetime or constrained to move within a spherical box. We show that this simple two-body system has surprisingly rich dynamics, which includes prompt collapse to a black hole, perpetually oscillating solutions or black hole formation at arbitrarily large times. Collapse is induced by shell crossing and the black hole mass depends sensitively on the number of shell crossings. At certain critical points, the black hole mass exhibits critical behavior, determined by the change in parity (even or odd) of the number of crossings, with or without mass-gap during the transition. Some of the features we observe are reminiscent of confined scalars undergoing "turbulent" dynamics.