Sinha, Monika

The existence of compact stars with high mass (> 2 M⊙ ) raises the possibility of the appearance of heavy baryons at high-density regimes.With this possibility, we study the effect of a strong magnetic field on the matter composed of baryon-octet and Δ -resonances under strong magnetic fields.The functionals in the hyperonic sector are constrained by the Λ, Ξ- hypernuclei data from terrestrial experiments.Δ -resonance sector is constrained by studies of their scattering off nuclei and heavy-ion collisions.The main effect of the magnetic field is shown to be the oscillations of various matter properties, viz., particle populations and Dirac effective mass with density resulting from the occupation of the Landau level by charged fermions in strong magnetic fields.

Compact stars with strong magnetic fields (magnetars) have been observationally determined to have surface magnetic fields of order of 1014-1015 G, the implied internal field strength being several orders larger. We study the equation of state and composition of dense hypernuclear matter in strong magnetic fields in a range expected in the interiors of magnetars. Within the non-linear Boguta-Bodmer-Walecka model we find that the magnetic field has sizable influence on the properties of matter for central magnetic field B ≥ 1017 G, in particular the matter properties become anisotropic. Moreover, for the central fields B ≥ 1018 G, the magnetized hypernuclear matter shows instability, which is signalled by the negative sign of the derivative of the pressure parallel to the field with respect to the density, and leads to vanishing parallel pressure at the critical value Bcr ≃ 1019 G. This limits the range of admissible homogeneously distributed fields in magnetars to fields below the critical value Bcr. © 2012 Elsevier B.V..

Magnetars are comparatively young neutron stars with ultra-strong surface magnetic field in the range 1014-1016G. The old neutron stars have surface magnetic field somewhat less 108G which clearly indicates the decay of field with time. One possible way of magnetic field decay is by ambipolar diffusion. We describe the general procedure to solve for the ambipolar velocity inside the star core without any approximation. With a realistic model of neutron star, we determine the ambipolar velocity configuration inside the neutron star core and hence find the ambipolar decay rate, associated timescales and the magnetic energy dissipated which is consistent with the magnetar observations.