Probing the Binary Black Hole Merger Regime with Scalar Perturbations

TL;DR

This study investigates scalar field scattering off binary black hole mergers, revealing early quasinormal ringing and providing a novel way to estimate black hole parameters during the merger process.

Contribution

It introduces a method to probe the merger regime using scalar perturbations and compares scalar-based measurements with dynamical horizon calculations.

Findings

Scalar fields exhibit quasinormal ringing earlier than gravitational wave signals.

Scalar quasinormal frequencies can estimate black hole mass and spin during merger.

Compatibility observed between scalar-based measures and horizon-based parameters.

Abstract

We present results obtained by scattering a scalar field off the curved background of a coalescing binary black hole system. A massless scalar field is evolved on a set of fixed backgrounds, each provided by a spatial hypersurface generated numerically during a binary black hole merger. We show that the scalar field scattered from the merger region exhibits quasinormal ringing once a common apparent horizon surrounds the two black holes. This occurs earlier than the onset of the perturbative regime as measured by the start of the quasinormal ringing in the gravitational waveforms. We also use the scalar quasinormal frequencies to associate a mass and a spin with each hypersurface, and observe the compatibility of this measure with the horizon mass and spin computed from the dynamical horizon framework.