Magnetic Field Effects on the Structure of Neutron Stars

We investigate the impact of ultrastrong magnetic fields on the structure of neutron stars within a density-dependent relativistic mean-field framework (DDME2). In the first case, we incorporate a magnetic field framework through Landau quantization of charged particles, yielding anisotropic pressure contributions and showing that field-induced stiffening increases stellar radii, maximum masses, and tidal deformabilities. To capture anisotropic stresses and geometric distortions, we employ axisymmetric equilibrium configurations computed with the XNS 4.0 code under the extended conformally flat condition. For magnetic field strengths up to 4.5×1017 G, we analyze purely poloidal and toroidal geometries across a representative mass range (1.2–2.0 M⊙). Axisymmetric models reveal that purely toroidal fields induce prolate deformations reaching |e¯| ≈0.67 for a 1.2 M⊙ star, while purely poloidal fields drive oblate deformations with e¯≈0.24, both diminishing with increasing stellar mass as greater gravitational binding resists magnetic reshaping. These macroscopic effects, combined with microphysical stiffening, have direct implications for gravitational-wave emission and systematic biases in radius measurements. Our study provides a systematic mapping between magnetic field strength, topology, and dense-matter stiffness, offering constraints relevant to multimessenger observations of magnetized neutron stars.