Using pulsar's braking indices to estimate changes in their moments of inertia with age-related considerations

Pulsars are modeled as neutron stars originated from the collapse of a progenitor one. In the canonical model they are described by spherical magnetized dipoles that rotate with the magnetic axis usually misaligned relative to the rotation axis, and such misalignment would explain the observation of radiation emitted in pulses in a certain direction rendering the typical observational characteristic of this kind of star. The frequency of such pulses decays with time and it can be quantified by the braking index (n). In the canonical model n = 3 for all pulsars but observational data show that n [negationslash] = 3. In this work we present a model for the understanding of the frequency decay of the rotation of a pulsar adapting the canonical one. We consider the pulsar a star that rotates in vacuum and has a strong magnetic field but, in contrast to the canonical model, we assume that its moment of inertia changes in time due to a uniform variation of a displacement parameter in time. We found that the old pulsars that present high values of the braking index tend to present smaller internal displacements of mass, in particular the superfluid neutron matter in the core. We relate this trend to neutron vortices' creep in rotating superfluids, indicating a possible reason for this coincidence. (paper)