Probing geometrically perturbed strange stars with minimal decoupling using millisecond pulsar timing observations

Abstract

We construct a gravitationally decoupled anisotropic strange star model using the minimal geometric deformation approach with a MIT bag equation of state and an additional source sector controlled by a deformation parameter ${\hat{I}}^2$ and a radial perturbation scale $\hat{I}¨$ through $g(r)=\sin (\hat{I}¨r^2)$. The resulting Einstein system is consistently split into seed and $\hat{I}¸$-sectors and matched to an exterior Schwarzschild geometry. The model is constrained by high-mass pulsars: PSR J0740+6620 $(2.08\pm 0.07M_{\odot })$, PSR J1810+1744 $(2.13\pm 0.04M_{\odot })$, PSR J1959+2048 $(2.18\pm 0.09M_{\odot })$, and PSR J2215+5135 $(2.28_{-0.09}^{+0.10}{M}_{\odot })$. It reproduces these objects with predicted radii $R\approx 11.3$--$12.9$ km. The maximum mass reaches $M_{\max }\approx 2.28M_{\odot }$ for ${\hat{I}}^2=3\times 10^{-3}$ and $\hat{I}¨\approx 0.03{\text{km}}^{-2}$, while for ${\hat{I}}^2=10^{-3}$ the configuration yields $M_{\max }\approx 2.12M_{\odot }$ with $R\approx 12.2$ km. The central density lies in $\ddot{I}{}_c\approx (2.4$--$3.1)\times 10^{-4}{\text{km}}^{-2}$, decreasing smoothly to $\ddot{I}{}_s\approx 2.0\times 10^{-4}{\text{km}}^{-2}$. The anisotropy increases from zero at the center to $\hat{I}”\approx (0.25$--$0.45)\times 10^{-4}{\text{km}}^{-2}$ near the surface, generating additional outward support that enhances compactness by $\sim 15\%$. The compactness parameter spans $C\approx 0.17$--$0.22$, safely below the Buchdahl limit, while the surface redshift reaches $z_s\approx 0.25$--$0.38$. The condition $dM/d\ddot{I}{}_c>0$ is satisfied throughout, confirming dynamical stability. Overall, ${\hat{I}}^2$ enhances the maximum mass by up to $\sim 15\%$, while $\hat{I}¨$ introduces controlled oscillatory structure without violating observational constraints, producing stable ultra-compact stars consistent with current pulsar data.

31 pages, 8 figures