Elastic stars in general relativity: IV. Axial perturbations

Abstract

This is the fourth paper in a series that attempt to put forward a consistent framework for modelling solid regions in neutron stars. Here we turn our attention to axial perturbations of spherically symmetric spacetimes using a gauge invariant approach due to one of us. Using the formalism developed in the first paper in the series it turns out that the matter perturbations are neatly expressible in terms of a ``metric'' tensor field depending only on the speeds of shear wave propagation along the principal directions in the solid. The results are applicable to a wide class of elastic materials and does not assume material isotropy nor quasi-Hookean behaviour. The perturbation equations are then specialised to a static background and are given by two coupled wave equations. Our formalism is thus slightly simpler than the previously existing results of Shumaker & Thorne, where an additional initial value equation needs to be solved. The simplification is mainly due to the gauge invariance of our approach and shows up also in somewhat simpler boundary conditions. We also give a first order formulation suitable for numerical integration of the quasi-normal mode problem of a neutron star. The relations between the gauge independent variables and the, in general, gauge dependent perturbed metric and strain tensor are explicitly given.

18 pages, no figures

References in corpus (6)

• Neutron Star Asteroseismology. Axial Crust Oscillations in the Cowling Approximation
• Torsional Oscillations of Relativistic Stars with Dipole Magnetic Fields
• QPOs during magnetar flares are not driven by mechanical normal modes of the crust
• On the theory of magnetar QPOs
• Elastic or magnetic? A toy model for global magnetar oscillations with implications for QPOs during flares
• Relativistic mechanics of neutron superfluid in (magneto) elastic star crust

Cited by in corpus (9)

• Crustal Oscillations of Slowly Rotating Relativistic Stars
• Axial quasi-normal modes of neutron stars: Accounting for the superfluid in the crust
• A characteristic approach to the quasi-normal mode problem
• Cylindrically symmetric static solutions of the Einstein field equations for elastic matter
• Linearizing a Non-linear Formulation for General Relativistic Dissipative Fluids
• Magneto-elastic torsional oscillations of magnetars
• Extended body dynamics in general relativity: hyperelastic models
• Elastic thick shells in General Relativity
• Encounter between an extended hyperelastic body and a Schwarzschild black hole with quadrupole-order effects