ROTATING NEUTRON-STAR MODELS WITH A MAGNETIC-FIELD

We present the first numerical solutions of the coupled Einstein-Maxwell equations describing rapidly rotating neutron stars endowed with a magnetic field. These solutions are fully relativistic and self-consistent, all the effects of the electromagnetic field on the star's equilibrium (Lorentz force, spacetime curvature generated by the electromagnetic stress-energy) being taken into account. The magnetic field is axisymmetric and poloidal. Five dense matter equations of state are employed. The partial differential equation system is integrated by means of a pseudo-spectral method. Various tests passed by the numerical code are presented. The effects of the magnetic field on neutron stars structure are then investigated, especially by comparing magnetized and non-magnetized configurations with the same baryon number. The deformation of the star induced by the magnetic field is important only for huge values of B (B > 10(10) T). The maximum mass as well as the maximum rotational velocity are found to increase with the magnetic field. The maximum allowable poloidal magnetic field is of the order of 10(14) T and is reached when the magnetic pressure is comparable to the fluid pressure at the centre of the star. For such values, the maximum mass of neutron stars is found to increase by 13 to 29% (depending upon the EOS) with respect to the maximum mass of non-magnetized stars.