Constraining linear form of f(R,G,T) gravity from astrophysical observations of the Pulsar U1724

Document Type

Article

Publication Date

9-2025

Abstract

This study explores the structure of compact stars using an extended theory of gravity known as f(R,G,T) gravity, where R, is the Ricci scalar, G, the Gauss-Bonnet invariant, and T the trace of the energy-momentum tensor. Focusing on massive radio pulsars, specifically neutron stars with masses greater than 1.8 solar masses, utilize these extreme astrophysical environments to test gravity in regimes unreachable by Earth-based experiments. We adopt a linear form of the theory, f(R,G,T)=R+αG+βT, with α,1 and β are dimensional constants, and derive an exact analytical solution for anisotropic perfect fluid spheres in hydrostatic equilibrium. This model incorporates the compactness factor C=[Formula presented], to describe all physical properties within the stellar interior. To constrain the model, we employ observational data from the pulsar U1724, using its mass and radius to fix the parameters at their upper bounds: α1=[Formula presented]=±0.023 and β1=[Formula presented]=±0.001. The resulting model is consistent with physical viability and observational constraints. Notably, the squared sound speed in this framework remains below the theoretical limit (cs22/3), contrasting with general relativity results. Without assuming a specific equation of state, the model exhibits linear behavior and predicts a core density several times higher than nuclear saturation density (ρnuc=2.6×1014 g/cm3), with surface density ρs, also exceeding this threshold. Additionally, the derived mass-radius relation agrees well with existing astrophysical observations.

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