Axial quasi-normal modes of neutron stars: Accounting for the superfluid in the crust

Abstract

We present the results of the first study of global oscillations of relativistic stars with both elastic crusts and interpenetrating superfluid components. For simplicity, we focus on the axial quasi-normal modes. Our results demonstrate that the torsional crust modes are essentially unaffected by the coupling to the gravitational field. This is as expected since these oscillations are known to be weak gravitational-wave sources. In contrast, the presence of a loosely coupled superfluid neutron component in the crust can have a significant effect on the oscillation spectrum. We show that the entrainment between the superfluid and the crust nuclei is a key parameter in the problem. Our analysis highlights the need for a more detailed understanding of the coupled crust-superfluid at the microphysical level. Our numerical results have, even though we have not considered magnetised stars, some relevance for efforts to carry out seismology based on quasi-periodic oscillations observed in the tails of magnetar flares. In particular, we argue that the sensitive dependence on the entrainment may have to be accounted for in attempts to match theoretical models to observational data.

19 pages

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Cited by in corpus (10)

• Neutron conduction in the inner crust of a neutron star in the framework of the band theory of solids
• Relativistic fluid dynamics: physics for many different scales
• Spectrum of shear modes in the neutron-star crust: Estimating the nuclear-physics uncertainties
• Universal relation for supernova gravitational waves
• Unified description of neutron superfluidity in the neutron-star crust with analogy to anisotropic multi-band BCS superconductors
• Quasi-normal modes of superfluid neutron stars
• Quasi-periodic oscillations in superfluid, relativistic magnetars with nuclear pasta phases
• Non-radial pulsations of gravitationally coupled two-fluid neutron stars in general relativity
• A gravitational-wave perspective on neutron-star seismology
• Axial Gravitational Normal Modes of Uniform Density Star in Anti-de Sitter Spacetime