Novel Stellar Astrophysics from Extended Gravity

TL;DR

This paper explores how extended theories of gravity can better explain the existence of large-mass neutron stars in the mass-gap region, reconciling gravitational wave observations with astrophysical models.

Contribution

It critically examines the role of extended gravity theories in explaining massive neutron stars and discusses implications for the maximum neutron star mass.

Findings

Extended gravity models can support larger neutron star masses.

Standard GR requires extremely stiff EoS for large masses, conflicting with observations.

Extended gravity may reconcile GW observations with neutron star physics.

Abstract

Novel implications on neutron stars come from extended gravity. Specifically, the GW190814 event indicated the probability of having large mass stars in the mass-gap region $2.5-5\, M_{\odot}$. If the secondary component of GW190814 is a neutron star, such large masses are marginally supported by General Relativity (GR), since a very stiff Equation of State (EoS) would be needed to describe such large mass neutron stars, which would be incompatible with the GW170817 event, without any modification of gravity. In view of the two groundbreaking gravitational wave observations, we critically discuss the elevated role of extensions of GR towards the successful description of the GW190814 event, and we also speculate in a quantitative way on the important issue of the largest allowed neutron star mass.