(Self-)Magnetized Bose–Einstein condensate stars

Abstract

We study magnetic field effects on the Equations-of-State (EoS) and the structure of Bose–Einstein Condensate (BEC) stars, i.e. a compact object composed by a gas of interacting spin-one bosons formed up by the pairing of two neutrons. To include the magnetic field in the thermodynamic description, we assume that particle–magnetic field and particle–particle interactions are independent. We consider two configurations for the magnetic field: one where it is constant and externally fixed, and another where it is produced by the bosons through self-magnetization. Stable configurations of self-magnetized and magnetized nonspherical BEC stars are studied using structure equations that describe axially symmetric objects. In general, the magnetized BEC stars are spheroidal, less massive and smaller than the nonmagnetic ones, being these effects more relevant at low densities. Nevertheless, star masses around two solar masses are obtained by increasing the strength of the boson–boson interaction. The inner magnetic field profiles of the self-magnetized BEC stars can be computed as a function of the equatorial radii. The values obtained for the core and surface magnetic fields are in agreement with those typically found in compact objects.