Semianalytical estimates of scattering thresholds and gravitational radiation in ultrarelativistic black hole encounters

TL;DR

This paper uses semianalytical methods to analyze gravitational radiation and scattering thresholds in ultrarelativistic black hole collisions, complementing numerical relativity results and exploring effects of spin and spacetime dimensions.

Contribution

It introduces two semianalytical approaches to estimate gravitational radiation and scattering thresholds in black hole encounters, enhancing understanding beyond numerical simulations.

Findings

Energy spectra explained by zero-frequency limit analysis.

Near-critical regime multipolar radiation structure characterized.

Dependence of scattering threshold on spin and dimensions qualitatively estimated.

Abstract

Ultrarelativistic collisions of black holes are ideal gedanken experiments to study the nonlinearities of general relativity. In this paper we use semianalytical tools to better understand the nature of these collisions and the emitted gravitational radiation. We explain many features of the energy spectra extracted from numerical relativity simulations using two complementary semianalytical calculations. In the first calculation we estimate the radiation by a "zero-frequency limit" analysis of the collision of two point particles with finite impact parameter. In the second calculation we replace one of the black holes by a point particle plunging with arbitrary energy and impact parameter into a Schwarzschild black hole, and we explore the multipolar structure of the radiation paying particular attention to the near-critical regime. We also use a geodesic analogy to provide qualitative estimates of the dependence of the scattering threshold on the black hole spin and on the dimensionality of the spacetime.