Observational Constraints on the Maximum Masses of White Dwarfs, Neutron Stars, and Exotic Stars in Non-Minimal Derivative Coupling Gravity

Abstract

The advancement of astronomical observations opens the possibility of testing our current understanding of gravitational theory in the strong-field regime and probing any deviation from general relativity. We explore to what extent compact stars predicted by non-minimal derivative coupling (NMDC) gravity theory agree with observed data. We investigate white dwarfs (WDs), neutron stars (NSs), and quark stars (QSs) mass and radius in various values of constant scalar $|Q_{\infty}|$ at coupling strength of $\eta=\pm1$. This study focuses on the astrophysical impacts of altering maximum masses by values of $|Q_{\infty}|$ and $\eta$. From an observational point of view, we found that WD stars are consistent with ultra-cold WD data at $|Q_{\infty}| \lesssim 0.2$. We also found that QS has a similar impact of mass-radius to NS, where the modification is more significant at higher (central) density. For NS and QS EoSs, the value $|Q_{\infty}|$ strongly alters the critical mass and might eliminate the $M-\rho_c$ turning point in the negative $\eta$ case. In that case, the sufficiently large $|Q_{\infty}|$ could predict $M>2.6 M_\odot$ NS and QS, i.e., larger than GW190814 secondary counterpart. We suggest that the lower mass gap in the gravitational wave and x-ray binary mass population data might restrict the theory's $|Q_{\infty}|$.