Dynamical descalarization with a jump during black hole merger

TL;DR

This paper investigates how black hole mergers in scalar-Gauss-Bonnet gravity can cause a sudden loss of scalar hair, producing distinctive gravitational wave signals similar to phase transitions in neutron star mergers.

Contribution

It demonstrates through simulations that dynamical descalarization can produce observable jumps in gravitational wave signals during black hole mergers.

Findings

Jump in scalar hair during black hole merger observed in simulations

Distinct gravitational wave signatures identified for descalarization events

Potential to distinguish scalar-Gauss-Bonnet effects in gravitational wave data

Abstract

Black holes in scalar-Gauss-Bonnet gravity are prone to scalarization, that is a spontaneous development of scalar hair for strong enough spacetime curvature while the weak field regime of the theory coincides with general relativity. Since large spacetime curvature is associated with smaller black hole masses, the merging of black holes can lead to dynamical descalarization. This is a spontaneous release of the scalar hair of the newly formed black hole in case its mass is above the scalarization threshold. Depending on the exact form of the Gauss-Bonnet coupling function, the stable scalarized solutions can be either continuously connected to the Schwarzschild black hole, or the transitions between the two can happen with a jump. By performing simulations of black hole head-on collisions in scalar-Gauss-Bonnet gravity prone to dynamical descalization, we have demonstrated that such a jump can be clearly observed in the accumulated gravitational wave data of multiple merger events with different masses. The distinct signature in the gravitational wave signal will share similarities with the effects expected from first order matter phase transitions happening during neutron star binary mergers.