Cosmic condensates - vortex, fluxtube and neutron star dynamics

Abstract

This thesis studies the implications of cosmic condensates, specifically the dynamics of superfluid vortices and superconducting fluxtubes, on astrophysical observables. Firstly, several mutual friction forces, arising from the interactions of vortices and their surroundings, are examined. We separately address mesoscopic mechanisms acting in the neutron star core and crust and analyse the strength of the resulting macroscopic mutual friction for realistic equations of state. It is obtained that the coupling strengths vary significantly within both layers and the dissipation changes drastically across the crust-core boundary. In analogy with helium experiments, the interface should therefore have important implications for the stars’ rotational properties.

This is followed by an analysis of mechanisms affecting the superconducting flux-tubes. Their motion governs the dynamics of the interior magnetic field and characteristic evolution timescales are presented for a realistic equation of state. While these results are only preliminary and a more detailed analysis of additional processes is needed, they point towards deficiencies in earlier work on this subject. Subsequently, one of the flux-tube mechanisms is investigated in more detail and the analogy with normal magneto-hydrodynamics is employed to derive a superconducting induction equation. While this equation differs significantly from the normal resistive equivalent, several key notions of standard magnetohydrodynamics are retained. From the field evolution equation we further deduce that the canonical fluxtube dissipation is not strong enough to explain field evolution timescales invoked from observations. To reconcile these, entirely different fluxtube coupling mechanisms are required.

Finally, the possibility of using laboratory condensates to study aspects of neutron star physics, only poorly understood, is examined. Specifically helium, ultra-cold gases and superconductors are prime candidates to mimic the behaviour of neutron stars on smaller scales. By looking at typical characteristics such as the two-fluid nature, super-fluid turbulence and pinning, we find that terrestrial quantum states could provide a promising new angle to fill the missing pieces of neutron star astrophysics.

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Identifiers

ORCID for Nils Andersson: orcid.org/0000-0001-8550-3843

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