Sinha, Monika

Compact stars having strong magnetic fields (magnetars) have been observationally determined to have surface magnetic fields of order of 10 14-1015 G, the implied internal field strength being several orders larger. We study the equation of state and composition of hypernuclear matter and quark matter - two forms of dense matter in strong magnetic fields. We find that the magnetic field has substantial influence on the properties of hypernuclear matter and quark matter for magnetic field B ≥ 1017 G and B ≥ 1018 G respectively. In particular the matter properties become anisotropic. Moreover, above a critical field B cr, both hypernuclear and quark matter show instability, although the values of Bcr are different for two kinds of matter. © Published under licence by IOP Publishing Ltd.

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.

The magnetars are believed to be highly magnetized neutron stars having surface magnetic field 1014 − 1015 G. It is believed that at the center, the magnetic field may be higher than that at the surface. We study the effect of the magnetic field on the neutron star matter. We model the nuclear matter with the relativistic mean field approach considering the possibility of appearance of hyperons at higher density. We find that the effect of magnetic field on the matter of neutron stars and hence on the mass-radius relation is important, when the central magnetic field is atleast of the order of 1017 G. Very importantly, the effect of strong magnetic field reveals anisotropy to the system. Moreover, if the central field approaches 1019 G, then the matter becomes unstable which limits the maximum magnetic field at the center of magnetars.

MeV-scale magnetic fields in the interiors of magnetars suppress the pairing of neutrons and protons in the S-wave state. In the case of a neutron condensate the suppression is the consequence of the Pauli-paramagnetism of the neutron gas, i.e., the alignment of the neutron spins along the magnetic field. The proton S-wave pairing is suppressed because of the Landau diamagnetic currents of protons induced by the field. The Ginzburg-Landau and BCS theories of the critical magnetic fields for unpairing are reviewed. The macrophysical implications of the suppression (unpairing) of the condensates are discussed for the rotational crust-core coupling in magnetars and the neutrino-dominated cooling era of their thermal evolution.