Weighing massive neutron star with screening gravity: A look on PSR J0740+6620 and GW190814 secondary component

TL;DR

This paper explores how modified gravity, specifically screening effects, can allow neutron stars with soft equations of state to reach high masses, explaining observations like GW190814's secondary component and PSR J0740+6620.

Contribution

It demonstrates that incorporating screening gravity effects can reconcile soft EoSs with the existence of massive neutron stars, challenging previous constraints.

Findings

Screening gravity can increase maximum neutron star mass.

Soft EoSs are compatible with high-mass NSs when gravity effects are considered.

High-mass NSs can be explained without ruling out soft EoSs.

Abstract

Neutron stars (NSs) are excellent natural laboratories to constrain gravity on strong field regime and nuclear matter in extreme conditions. Motivated by the recent discovery of a compact object with $2.59^{+0.08}_{-0.09} M_\odot$ in the binary merger GW190814, if this object was a NS, it serves as a strong constraint on the NS equation of state (EoS), ruling out several soft EoSs favored by GW170817 event. In this work, we revisit the question of the maximum mass of NSs considering a chameleon screening (thin-shell effect) on the NS mass-radius relation, where the microscopic physics inside the NS is given by realistic soft EoSs. We find that from appropriate and reasonable combination of modified gravity, rotation effects and realistic soft EoSs, that it is possible to achieve high masses and explain GW190814 secondary component, and in return also NSs like PSR J0740+6620 (the most NS massive confirmed to date). It is shown that gravity can play an important role in estimating maximum mass of NSs, and even with soft EoSs, it is possible to generate very high masses. Therefore, in this competition on the hydrostatic equilibrium between gravity and EoS, some soft EoSs, in principle, cannot be completely be ruled out without first taking into account gravitational effects.