Deformation of neutron stars due to poloidal magnetic fields

The mass-radius (MR) relation of deformed neutron stars in the axially symmetric poloidal magnetic field is calculated. TheMRrelation is obtained by solving the Hartle equations, whereas the one for spherical stars is obtained by the Tolman-Oppenheimer-Volkoff equations. The anisotropic effects of the poloidal magnetic fields are found to be non-negligible for a strong magnetic field more than 3 x 10(18) G at the center of a neutron star.