$2.6 M_\odot$ Compact Object and Neutron Stars within Eddington-Inspired Born-Infeld Theory of Gravity

TL;DR

This study explores how Eddington-inspired Born-Infeld gravity parameters influence neutron star properties and assesses whether a 2.6 solar mass object from GW190814 could be a neutron star within this framework, considering observational constraints.

Contribution

It demonstrates that within EiBI gravity, a 2.6 solar mass neutron star is unlikely, highlighting the impact of gravity parameters on neutron star mass and radius predictions.

Findings

Neutron star mass depends strongly on the parameter κ.

Radius is sensitive to the cosmological constant Λ_c.

A 2.6 M_sun object cannot be a neutron star within this theory under realistic conditions.

Abstract

In the context of whether a massive compact object recently observed in the GW190814 event is a neutron star (NS) or not, we have studied the role of the parameters $\kappa$ and $\Lambda_c$ of the Eddington-inspired Born-Infeld (EiBI) gravity theory on the NS mass-radius relation, moment of inertia, and tidal deformability. The results are compared to recent observation constraints extracted from the analysis of NS observation data. The NS core equation of state (EoS) is calculated using the relativistic mean-field model with the G3 parameter set. In the hyperon sector, the SU(3) and hyperon potential depths are used to determine the hyperon coupling constants. For the inner and outer crusts, we use the crust EoS from Miyatsu et al. (2013). We also maintain the sound speed to not exceed $c$/$\sqrt{3}$ at high densities. We have found that, in general, the NS mass significantly depends on the value of $\kappa$, and the radius $R$ is sensitive to the value of $\Lambda_c$. Moreover, as $\Lambda_c$ is equal to zero or less than the accepted bound of the cosmological constant, the NS within the EiBI theory is compatible with observation constraints, including $2.0 M_\odot$ mass, canonical radius $R_{1.4 M_{\odot}}$, moment of inertia, and tidal deformation. Our investigation also reveals that the $2.6 M_\odot$ mass compact object and current observational constraint of canonical radius $R_{1.4 M_{\odot}}$ can simultaneously be satisfied only when the $\Lambda_c$ value is unphysically too large and negative. Therefore, within the spesific EoS employed in this work, we conclude that the secondary object with $2.6 M_\odot$ observed in the GW190814 event is not likely a static (or a slow-rotating) NS within the EiBI gravity theory.