ADVANCES IN MODELS OF PULSAR GLITCHES

Neutron stars are surely one of the most interesting astronomical objects: in no other place of the observable universe, in fact, matter is so compressed that the density reaches and overcomes the nuclear saturation value. This is a so extreme condition that in no terrestrial laboratory we can directly reproduce it in order to study its properties. Neutron stars are therefore a very fascinating research field that can bring us to a deeper understanding of this exotic matter, by modeling the observations of peculiar phenomena related to these stars. This thesis is focused on the pulsar glitches, which are rapid jumps in the rotational velocity of the star. Shortly after the first glitches were observed it was suggested that they could be due to a superfluid component in the stellar interior that could store angular momentum thanks to the pinning interaction between superfluid vortexes and crustal lattice. This qualitative idea suggests that the problem must be faced by merging results which come from the microphysics point of view into a more macroscopic simulation. In this thesis we deal with the evaluation of the vortex--nuclei interaction from the mesoscopic point of view: we perform a realistic calculation of the pinning force per unit length for the inner crust of a neutron star. We find that this mesoscopic interaction is $\approx10^{15} \mbox{ dyn/cm}$, much smaller than previous calculations but still enough to explain glitches. A similar approach has been adopted also in the calculation of the pinning force in the core: if protons in the interior are in a type II superconducting state, an interaction between magnetic flux tubes and rotational vortexes is possible and must be estimated (in case of type I superconductivity the interactions are much weaker). Our results indicate that even in this case, the interaction between vortexes and flux tubes will be significantly weaker than in the crust, as the force per unit length is $\approx 10^{12} - 10^{13} \mbox{ dyn/cm}$. These results are used in static models (based on the "snowplow" model) which can reproduce the physical observable parameters and also provide a mean to infer the masses of the most frequent glitching stars: we propose a unified description of the glitch phenomenon both for small and large glitchers and we analyze the interesting correlation between mass and glitching strength. The whole temporal evolution of a glitch can be followed thanks to the development of a dynamical model. The multifluids formalism is implemented in a consistent simulation, which take into account realistic physical inputs like equation of state, entrainment and drag forces: the rise and the recovery of a glitch is analyzed in connection with the relevant parameters of the model, in order to understand more deeply all the aspects of this phenomenon. We also compare our simulations with the observational data of the frequent glitchers in order to estimate the masses of the pulsars. It's noteworthy the fact that the results are in good agreement with the ones obtained with the static approach, showing again the same mass--glitching strength relation.