Neutron stars and their terrestrial analogues

Abstract

When we consider in detail the behaviour of a fluid consisting of two (or possibly more) interpenetrating components, the likelihood of dynamical instabilities induced by coupling between the two fluids cannot be ignored. The phenomenon is generic to all such multi fluid systems and as such is appellated the two-stream instability. Mathematically this class of instability is somewhat akin to the more well known Kelvin Helmholtz instability, but is distinguished by the fluids flowing through each other rather than having a clearly defined interface between them. In this thesis we describe in some detail the mechanisms underlying this instability in a simple linear flow scrutinising in particular the growing (unstable) solutions for small harmonic perturbations. We further consider the application of this genre of instabilities to other physical systems, most conspicuously to that of a rotating super fluid body with rotational lag between the components. This case is of particular interest in neutron star physics, where it offers possibilities for exploring behaviour within the core. There also seems to be the chance of exploring this example in laboratory systems. We also take a tentative first step to extending the application and understanding of the two-stream instability by flirting with the analogous observations in a laboratory realisable binary Bose-Einstein Condensate. This laboratory realisation is a first step towards being able to explore physically issues relating to neutron star dynamics. We further discuss general analogue systems for modelling key features of neutron stars in terrestrial laboratories. The possible applications, along with some of the diffculties in using these analogues, are explored.

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

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