Binary neutron star mergers in massive scalar-tensor theory: Properties of post-merger remnants

TL;DR

This study uses numerical relativity to explore how massive scalar-tensor gravity affects binary neutron star merger remnants, revealing increased threshold mass for collapse and unique gravitational wave signatures.

Contribution

It introduces new insights into post-merger neutron star properties within massive scalar-tensor theories, highlighting effects of scalar fields on stability and gravitational wave signals.

Findings

Threshold mass for prompt collapse is increased by scalar field.

Existence of long-lived scalar-induced oscillation modes in remnants.

Distinctive gravitational wave signatures linked to scalar field effects.

Abstract

We investigate the properties of post-merger remnants of binary neutron star mergers in the framework of Damour-Esposito-Farese-type scalar-tensor theory of gravity with a massive scalar field by numerical relativity simulation. It is found that the threshold mass for prompt collapse is raised in the presence of the excited scalar field. Our simulation results also suggest the existence of long-lived $\phi-$mode in hypermassive neutron stars due to the presence of the massive scalar field which enhances the quasi-radial oscillation in the remnant. We investigate the descalarization condition in hypermassive neutron stars and discover a distinctive signature in post-merger gravitational waves.