From mergers to collapse: scalarisation dynamics in neutron star binaries

TL;DR

This paper presents the first fully non-linear simulations of binary neutron star mergers in Einstein-scalar-Gauss-Bonnet gravity, revealing new phenomena like enhanced prompt collapse and scalarisation instabilities.

Contribution

It introduces the first non-linear evolutions of neutron star mergers in a modified gravity theory, exploring scalarisation effects beyond General Relativity.

Findings

Enhanced prompt collapse in certain scalar-Gauss-Bonnet couplings

Development of scalar configurations due to instabilities

New post-merger phenomena in modified gravity context

Abstract

We present the first fully non-linear evolutions of binary neutron star mergers in a moving-punctures approach in Einstein-scalar-Gauss-Bonnet gravity. We study both linear and quadratic-type couplings between the scalar and the Gauss-Bonnet invariant, and uncover new post-merger phenomena. These include an enhancement of the prompt collapse of a long-lived hyper-massive neutron star remnant and cases where the remnant develops a scalar configuration due to different scalarisation instabilities. This study initiates the exploration of beyond-General-Relativistic effects enhanced by the non-linear dynamics of the neutron star's fluid.