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Astrophysics, Solar and Stellar Astrophysics, astro-ph.SR,General Relativity and Quantum Cosmology, gr-qc
Abstract:
Understanding the properties of the internal magnetic field of neutron stars
remains a theoretical challenge. Over the last years, twisted-torus geometries
have been considered both in Newtonian and general-relativistic equilibrium
models, as they represent a potentially good description of neutron star
interiors. All of these works have found an apparent intrinsic limitation to
geometries that are poloidal-field-dominated, with a toroidal-to-poloidal
energy ratio inside the star that are <10%, unless surface currents are
included and magnetic fields are allowed to be discontinuous. This limitation
is in stark contrast with the general expectation that much higher toroidal
fields should be present in the stellar interior and casts doubt about the
stability and hence realism of these configurations. We here discuss how to
overcome this limitation by adopting a new prescription for the azimuthal
currents that leads to magnetized equilibria where the toroidal-to-total
magnetic-field energy ratio can be as high as 90%, thus including geometries
that are toroidal-field-dominated. Moreover, our results show that for a fixed
exterior magnetic-field strength, a higher toroidal-field energy implies a much
higher total magnetic energy stored in the star, with a potentially strong
impact on the expected electromagnetic and gravitational-wave emission from
highly magnetized neutron stars.
