Dynamical hair growth in black hole binaries in Einstein-scalar-Gauss-Bonnet gravity

TL;DR

This paper investigates how binary black holes in Einstein-scalar-Gauss-Bonnet gravity can acquire scalar charges during inspiral, potentially observable through gravitational waves, using semi-analytic models and numerical simulations.

Contribution

It introduces a semi-analytic model for dynamical scalarization and confirms findings with numerical relativity simulations, highlighting potential observational signatures.

Findings

Binary black holes can develop scalar charges during inspiral.

The scalarization effect is detectable with future gravitational-wave detectors.

The model aligns with numerical relativity results, validating the approach.

Abstract

Within the framework of scalar-tensor theories of gravity, certain models can evade classical black hole no-hair theorems. A well-known example is Einstein-scalar-Gauss-Bonnet gravity, where black holes carrying a scalar charge can exist. We find that, within this theory, binary black holes initially described by General Relativity can acquire scalar charges once they reach a critical orbital separation ("dynamical scalarization"). We develop a simple semi-analytic model, based on the adiabatic conservation of the total Wald entropy, to estimate the scalar charge evolution during the binary inspiral. We also run fully nonlinear numerical-relativity simulations for different configurations, finding consistent results. The gravitational-wave phase difference between Einstein-scalar-Gauss-Bonnet and General Relativity waveforms, which we use to assess detectability, is also computed. We find that dynamical scalarization might be observable in nearly equal-mass binary black hole mergers with third-generation ground-based gravitational-wave detectors, in a narrow range of the dimensional coupling of the theory.