Dark matter stars from beyond General Relativity models: Magnetosphere dynamics and torsion fields

Abstract

The magnetosphere structure of compact objects is considered in the context of a theory of gravity with dynamical torsion field beyond standard General Relativity (GR) introduced previously in Cirilo-Lombardo and Minotti (2019). To this end, a new spherically symmetric solution is obtained. A particular case physically representing a compact object of pseudoscalar fields (for example, axion field) is analyzed from the magnetosphere dynamics viewpoint using the axially symmetric version of the Grad-Shafranov equation (GSE) previously derived. We explicitly show that, in sharp contrast with the dipole case, the quadrupole case (where we have two well defined toroidal lobes) the energy stored in the magnetosphere increases more than in the pure dipole case, fact that is important to explain the problem of excess energy in mechanics of the pulsars and in the structure of magnetars. In this way we briefly discuss with the same argument as the one presented in Wang et al. (2019), how in our theoretical frame our model can help reinterpret phenomenological and observational results in the case of the X-ray emission of XTE J1810-197.