Strong-field tidal distortions of rotating black holes: II. Horizon dynamics from eccentric and inclined orbits

TL;DR

This paper extends previous work to analyze the horizon dynamics of Kerr black holes under tidal distortions caused by generic bound orbits, revealing complex horizon responses including offsets, bulging, and high-frequency oscillations.

Contribution

It introduces new tools for studying horizon geometry in generic orbits and uncovers novel features like horizon oscillations and offsets in the dynamical case.

Findings

Significant horizon bulging and offsets depend on orbit and spin.

Discovery of high-frequency oscillations in horizon response.

Horizon behavior features carry over from static to dynamical scenarios.

Abstract

In a previous paper, we developed tools for studying the horizon geometry of a Kerr black hole that is tidally distorted by a binary companion using techniques that require large mass ratios but can be applied to any bound orbit and allow for arbitrary black hole spin. We now apply these tools to generic Kerr black hole orbits. This allows us to investigate horizon dynamics: the tidal field perturbing the horizon's geometry varies over a generic orbit, with significant variations for eccentric orbits. Many of the features of the horizon's behavior found previously carry over to the dynamical case in a natural way. In particular, we find significant offsets between the applied tide and the horizon's response. This leads to bulging in the horizon's geometry which can lag or lead the orbit, depending upon the hole's rotation and the orbit's geometry. An interesting and apparently new feature we find are small-amplitude, high-frequency oscillations in the horizon's response. We have not been able to identify a mechanism for producing these oscillations, but find that they appear most clearly when rapidly rotating black holes are distorted by very strong-field orbits.