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Astrophysics, Solar and Stellar Astrophysics, astro-ph.SR,General Relativity and Quantum Cosmology, gr-qc
Abstract:
Recently, general relations among the quadrupole moment (Q), the moment of
inertia (I), and the tidal deformability (Love number) of a neutron star were
shown to exist. They are nearly independent of the nuclear matter equation of
state and would be of great aid in extracting parameters from observed
gravitational-waves and in testing general relativity. These relations,
however, do not account for strong magnetic fields. We consider this problem by
studying the effect of a strong magnetic field on slowly rotating relativistic
neutron stars and show that, for simple magnetic field configurations that are
purely poloidal or purely toroidal, the relation between Q and I is again
nearly universal. However, different magnetic field geometries lead to
different I-Q relations, and, in the case of a more realistic twisted-torus
magnetic field configuration, the relation depends significantly on the
equation of state, losing its universality. I-Love-Q relations must thus be
used with very great care, since universality is lost for stars with long spin
periods, i.e. P > 10 s, and strong magnetic fields, i.e. B > 10^12 G.
