Relativistic massive compact stars supported by decoupled matter: implications for mass-radius bounds

Abstract The merger of binary neutron stars (BNSs) is a remarkable astrophysical event where all four fundamental forces interplay dynamically across multiple stages, producing a rich spectrum of multi-messenger signals. These observations present a significant multiphysics modeling challenge but also offer a unique opportunity to probe the nature of gravity and the strong nuclear interaction under extreme conditions. The landmark detection of GW170817 provided essential constraints on the properties of non-rotating neutron stars (NSs), including their maximum mass ( M max ) and radius distribution, thereby informing the equation of state (EOS) of cold, dense nuclear matter. While the inspiral phase of such events has been extensively studied, the post-merger signal holds even greater potential to reveal the behavior of matter at supranuclear densities, particularly in scenarios involving a transition to deconfined quark matter. Motivated by the recent gravitational wave event GW190814 (2.5–2.67 M ⊙ ), we revisit the modeling of high-mass compact stars to investigate their internal structure via a generalized polytropic EOS. This framework incorporates a modified energy density profile and is coupled with the Tolman-Oppenheimer-Volkoff (TOV) equations. We explore mass-radius ( M – R ) relationships within both general relativity (GR) and the minimal geometric deformation (MGD) approach. Specifically, we constrain the radii of four massive compact objects — PSR J1614–2230 (1.97 +0.04 -0.04 M ⊙ ), PSR J0952–0607 (2.35 +0.17 -0.17 M ⊙ ), GW190814 (2.5–2.67 M ⊙ ), and GW200210 (2.83 +0.47 -0.42 M ⊙ ) — and demonstrate that our theoretical M – R curves are consistent with observational data. These findings provide meaningful constraints on the EOS and underscore the potential of alternative gravity models to accommodate ultra-massive compact stars within a physically consistent framework.