Constraining scalar-tensor theories of gravity from the most massive neutron stars

TL;DR

This paper investigates how the stability of highly compact neutron stars can constrain scalar-tensor theories of gravity, using nonlinear simulations and recent massive neutron star observations.

Contribution

It demonstrates that the dynamical instability of compact neutron stars can impose bounds on scalar-tensor gravity theories, complementing existing observational constraints.

Findings

Neutron star instability can lead to collapse in scalar-tensor theories.

Observations of massive neutron stars support bounds on scalar-tensor parameters.

The study links neutron star stability to fundamental gravity theories.

Abstract

Scalar-tensor~(ST) theories of gravity are natural phenomenological extensions to general relativity. Although these theories are severely constrained both by solar system experiments and by binary pulsar observations, a large set of ST families remain consistent with these observations. Recent work has suggested probing the unconstrained region of the parameter space of ST theories based on the stability properties of highly compact neutron stars. Here, the dynamical evolution of very compact stars in a fully nonlinear code demonstrates that the stars do become unstable and that the instability, in some cases, drives the stars to collapse. We discuss the implications of these results in light of recent observations of the most massive neutron star yet observed. In particular, such observations suggest that such a star would be subject to the instability for a certain regime; its existence therefore supports a bound on the ST parameter space.