Dynamics of spontaneous black hole scalarization and mergers in Einstein-scalar-Gauss-Bonnet gravity

TL;DR

This paper investigates the non-perturbative dynamics of black hole scalarization and mergers in Einstein-scalar-Gauss-Bonnet gravity, revealing conditions for stability, the influence of coupling choices, and scalar hair effects on gravitational waves.

Contribution

It provides the first comprehensive non-perturbative analysis of black hole scalarization dynamics, including stability conditions and merger outcomes in Einstein-scalar-Gauss-Bonnet theories.

Findings

Scalarization occurs for specific coupling signs and spins.

Stable scalarized black holes exist within a limited parameter range.

Scalar hair leaves detectable imprints on gravitational radiation.

Abstract

We study the dynamics of black holes in Einstein-scalar-Gauss-Bonnet theories that exhibit spontaneous black hole scalarization using recently introduced methods for solving the full, non-perturbative equations of motion. For one sign of the coupling parameter, non-spinning vacuum black holes are unstable to developing scalar hair, while for the other, instability only sets in for black holes with sufficiently large spin. We study scalarization in both cases, demonstrating that there is a range of parameter space where the theory maintains hyperbolic evolution and for which the instability saturates in a scalarized black hole that is stable without symmetry assumptions. However, this parameter space range is significantly smaller than the range for which stationary scalarized black hole solutions exist. We show how different choices for the subleading behavior of the Gauss-Bonnet coupling affect the dynamics of the instability and the final state, or lack thereof. Finally, we present mergers of binary black holes and demonstrate the imprint of the scalar hair in the gravitational radiation.