Neutron stars condense a mass comparable to that of the sun in a ten kilometre radius. As a consequence their interiors reach densities well above nuclear saturation density and allow to probe fundamental physics in regimes inaccessible to terrestrial experiments. Furthermore neutron stars are cold objects as, despite internal temperatures of tens of millions of degrees Kelvin, their thermal energy is negligible compared to their Fermi energy. This means that thermal excitations are too small to ‘free’ particles and allow them to interact. As a consequence, in the interior of a neutron star neutrons are superfluid and protons superconducting. Superfluidity has strong consequences on the dynamics of the star, as the superfluid can ‘flow’ relative to the `normal’ component of the star. A large scale, astrophysical, manifestation of superfluidity in neutron stars are pulsar glitches, sudden spin-ups observed in radio pulsars. Superfluidity, however, also has a strong impact on modes of oscillation of the neutron star. This is particularly interesting, as these modes can be probed with gravitational wave observations and allow to investigate the interior of the star, in much the same way as is done for our sun. These signals are, however, weak, and careful theoretical modelling is required to detect them and interpret them. This is a challenge, as one needs to understand how to extend quantum mechanical models of superfluid neutrons in the interior, on the scale of an atom, to the large scale dynamics of a 10 km star.
The aim of this project is to develop methods to bridge the gap in scales between microscopic modelling of neutron superfluids and large scale hydrodynamics models of pulsar glitches and gravitational wave emission. The models that have been developed allow to use astrophysical observations to obtain constrains on microphysical parameters and thus constrain the behaviour of matter at high densities.
The project contributes not only to our understanding of fundamental physics and the success of the LIGO/Virgo experiment, but also increases collaboration between different fields of Physics and between European institutions.
