Quark stars in energy-momentum squared gravity with recent astrophysical observations

Abstract

In this study, we explore the structural properties of quark stars (QSs) within the Energy-Momentum Squared Gravity (EMSG) framework, a modified gravity theory characterized by a quadratic coupling between the energy-momentum tensor and the spacetime geometry. By modifying the Tolman-Oppenheimer-Volkoff (TOV) equations, we analyze how the EMSG parameter alpha influences the mass-radius (M - R) and compactness (M - M/R) relations of QSs. Employing a quark matter equation of state (EoS) parameterized by the bag constant Beff and the interaction strength a4, we compute the hydrostatic equilibrium of QSs numerically. Our results reveal that negative alpha enhances the maximum mass of QSs, while positive alpha reduces it, consistent with previous findings. The study further demonstrates that increasing a4 stiffens the EoS, leading to larger radii and masses, while higher Beff softens the EoS, reducing the maximum mass. Stability analyses confirm that QS configurations satisfy the static stability criterion, adiabatic index constraints, and causality conditions. These findings align with astrophysical observations from events such as GW170817 and HESS J1731-347. This work establishes EMSG as a promising framework for studying compact stars under extreme physical conditions, and it paves the way for future research on rotating QSs, gravitational wave signatures, and phase transitions in modified gravity theories.