Hair is complicated: Gravitational waves from stable and unstable boson-star mergers

TL;DR

This study investigates gravitational waves from boson-star mergers, revealing they can emit more energy than black-hole collisions and exhibit sharp parameter-dependent features linked to star stability.

Contribution

It provides the first detailed analysis of gravitational-wave emission from boson-star mergers across a parameter space, highlighting unique energy features and stability effects.

Findings

Boson-star mergers can emit up to ten times more gravitational-wave energy than black-hole mergers.

The emitted energy shows sharp, discontinuous changes depending on star parameters.

Features are explained by the solitonic potential and stability properties of the stars.

Abstract

We explore the gravitational-wave emission from head-on collisions of equal-mass solitonic boson-star binaries from simulations spanning a two-dimensional parameter space, consisting of the central scalar-field amplitude of the stars and the solitonic potential parameter. We report the gravitational-wave energies emitted by boson-star binaries which, due to their combination of moderately high compactness with significant deformability, we often find to be louder by up to an order of magnitude than analogous black-hole collisions. The dependence of the radiated energy on the boson-star parameters exhibits striking needle-sharp features and discontinuous jumps to the value emitted by black-hole binaries. We explain these features in terms of the solitonic potential and the stability properties of the respective individual stars.