Structural Properties of Magnetized Neutron Stars under f (R, T ) Gravity Framework

TL;DR

This work investigates magnetized neutron stars within the linear $f(R,T)$ gravity framework $f(R,T)=R+2\lambda\kappa T$, solving the modified TOV equations using realistic EoSs (APR, FPS, SLy) and a central magnetic field up to $B_c=10^{18}$ G. The authors show that negative coupling $\lambda$ stiffens the stellar structure and increases the maximum mass (e.g., $M_{\max}$ approaching $2.7\,M_\odot$ for APR at $\lambda=-3/(8\pi)$), while strong central fields modestly decrease $M_{\max}$ by about $0.02\,M_\odot$ without breaking spherical symmetry. The resulting mass–radius relations remain compatible with NICER, PSR, and GW170817 constraints, indicating only modest deviations from GR in this strong-field regime. The study provides a self-consistent framework to probe modified gravity in ultra-dense, magnetized environments and outlines future extensions to tidal deformabilities, anisotropy, rotation, and higher-order curvature terms for richer observational tests.

Abstract

The current work investigates the structural properties of neutron stars in the presence of a strong magnetic field within the framework of f(R,T) modified gravity, where the matter-geometry coupling leads to deviations from general relativity at high matter densities. We present here the mass-radius sequences, as well as the mass and pressure distributions for various values of the modified gravity parameter and the central magnetic field. The modified Tolman-Oppenheimer- Volkoff equations are numerically solved using isotropic equations of state, specifically the APR, FPS, and SLy models. Comparing the corresponding results in the context of general relativity suggests that more negative values of the modified gravity parameter result in higher maximum gravitational masses. In contrast, strong central magnetic fields of up to 1018 Gauss cause only a slight decrease in maximum mass without disrupting spherical symmetry. Our findings are in agreement with the observed data from GW170817, PSR and NICER.

Figures (3)

• Figure 1: Mass vs radius profile for different neutron star equations of state (EoSs): (a) APR, (b) FPS and (c) SLy, both in the absence ($B_c = 0$) and presence $(B_c = 10^{18})$ Gauss of magnetic fields for the modified gravity parameter $\lambda$= $0$, $-\frac{1}{8\pi}$, $-\frac{2}{8\pi}$, and $-\frac{3}{8\pi}$, respectively. The cases without magnetic fields are labeled as ”WoB” (Without Magnetic field), and the cases with magnetic fields are labeled as ”WB” (With Magnetic field). Overlaid observational constraints: NICER J0030+0451 riley2019nicermiller2019psr, PSR J0348+0432 antoniadis2013massive and PSR J0740+6620 fonseca2021refinedcromartie2020relativistic, PSR J0952-0607 romani2022psr, PSR J1614-2230 demorest2010two and the blue and orange cloud region is the constraints for mass-radius from the GW170817 event, which was a merger of two neutron stars with an observation in the electromagnetic and gravitational spectrum abbott2018gw170817.
• Figure 2: The variation of mass with radial distance $r$ for different equations of state (EoS): (a) APR, (b) FPS, and (c) SLy, both in the presence ($B_c = 10^{18} \, \text{Gauss}$) and absence ($B_c = 0$) of magnetic fields for neutron stars of $1.4 \, M_\odot$. The cases without magnetic fields are labeled as "WoB" (Without Magnetic field), and the cases with magnetic fields are labeled as "WB" (With Magnetic field). The modified gravity parameter $\lambda$ is set to $0$, $-\frac{1}{8\pi}$, $-\frac{2}{8\pi}$, and $-\frac{3}{8\pi}$.
• Figure 3: The variation of pressure with radial distance $r$ for different equations of state (EoS): (a) APR, (b) FPS, and (c) SLy, both in the presence ($B_c = 10^{18} \, \text{Gauss}$) and absence ($B_c = 0$) of magnetic fields in neutron stars of $1.4 \, M_\odot$. The cases without magnetic fields are labeled as "WoB" (without magnetic field), and the cases with magnetic fields are labeled as "WB" (with magnetic field). The modified gravity parameter $\lambda$ is set to $0$ ,$-\frac{1}{8\pi}, -\frac{2}{8\pi}$, and $-\frac{3}{8\pi}$.