The Asymmetric Merger of Black Holes

TL;DR

This paper introduces a new geometric construction method for black hole event horizons, revealing that non-axisymmetric black holes often undergo a toroidal phase before merging into a spherical shape, highlighting features not seen in axisymmetric cases.

Contribution

It presents a novel approach to construct event horizon geometries directly, uncovering new features like the toroidal phase in non-axisymmetric black hole mergers.

Findings

Black holes often pass through a toroidal phase before becoming spherical.

The new method can produce event horizon geometries without relying on specific spacetime simulations.

Non-axisymmetric features differ significantly from axisymmetric cases.

Abstract

We study event horizons of non-axisymmetric black holes and show how features found in axisymmetric studies of colliding black holes and of toroidal black holes are non-generic and how new features emerge. Most of the details of black hole formation and black hole merger are known only in the axisymmetric case, in which numerical evolution has successfully produced dynamical space-times. The work that is presented here uses a new approach to construct the geometry of the event horizon, not by locating it in a given spacetime, but by direct construction. In the axisymmetric case, our method produces the familiar pair-of-pants structure found in previous numerical simulations of black hole mergers, as well as event horizons that go through a toroidal epoch as discovered in the collapse of rotating matter. The main purpose of this paper is to show how new - substantially different - features emerge in the non-axisymmetric case. In particular, we show how black holes generically go through a toroidal phase before they become spherical, and how this fits together with the merger of black holes.