dorsal/arxiv
View SchemaSpacetime Quasi-normal Mode Oscillations of Anisotropic Neutron Stars
| Authors | Jihao Yu, Victor Guedes, Shu Yan Lau, Siddarth Ajith, Kent Yagi |
|---|---|
| Categories | |
| ArXiv ID | 2601.06962vv1 |
| URL | https://arxiv.org/abs/2601.06962 |
| License | http://arxiv.org/licenses/nonexclusive-distrib/1.0/ |
Abstract
Neutron star asteroseismology offers a unique opportunity to probe nuclear physics through stellar oscillations. Although the pressure inside of a neutron star is typically assumed to be isotropic, pressure anisotropy can arise from various physical mechanisms, including elasticity, viscosity, and magnetic fields. Previous studies of nonradial stellar quasi-normal mode oscillations with anisotropic pressure have focused primarily on fluid modes. In this paper, we compute, for the first time, spacetime oscillation modes (so-called w-modes) of anisotropic neutron stars. Using a perturbative framework for stellar oscillations with pressure anisotropy, developed previously by some of the authors, together with a phenomenological anisotropy model, we find that both the real and imaginary parts of the w-mode frequencies decrease as the tangential pressure becomes dominant over the radial pressure. Although we do not find any unstable w-modes within the physically viable parameter space, unstable w-modes appear in an unphysical branch of solutions when the tangential pressure strongly dominates the radial one. We also find that the relation between the real part of the w-mode frequency and the stellar compactness is quasi-universal with respect to variations in the equation of state and the degree of pressure anisotropy. In contrast, the relation between the imaginary part of the w-mode frequency and the stellar compactness depends on the degree of anisotropy, but remains equation-of-state universal when the anisotropy is fixed. Finally, we discuss potential mode crossings and the validity of certain approximations that have been shown to work well for w-mode calculations in the isotropic case.
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"abstract": "Neutron star asteroseismology offers a unique opportunity to probe nuclear physics through stellar oscillations. Although the pressure inside of a neutron star is typically assumed to be isotropic, pressure anisotropy can arise from various physical mechanisms, including elasticity, viscosity, and magnetic fields. Previous studies of nonradial stellar quasi-normal mode oscillations with anisotropic pressure have focused primarily on fluid modes. In this paper, we compute, for the first time, spacetime oscillation modes (so-called w-modes) of anisotropic neutron stars. Using a perturbative framework for stellar oscillations with pressure anisotropy, developed previously by some of the authors, together with a phenomenological anisotropy model, we find that both the real and imaginary parts of the w-mode frequencies decrease as the tangential pressure becomes dominant over the radial pressure. Although we do not find any unstable w-modes within the physically viable parameter space, unstable w-modes appear in an unphysical branch of solutions when the tangential pressure strongly dominates the radial one. We also find that the relation between the real part of the w-mode frequency and the stellar compactness is quasi-universal with respect to variations in the equation of state and the degree of pressure anisotropy. In contrast, the relation between the imaginary part of the w-mode frequency and the stellar compactness depends on the degree of anisotropy, but remains equation-of-state universal when the anisotropy is fixed. Finally, we discuss potential mode crossings and the validity of certain approximations that have been shown to work well for w-mode calculations in the isotropic case.",
"arxiv_id": "2601.06962",
"authors": [
"Jihao Yu",
"Victor Guedes",
"Shu Yan Lau",
"Siddarth Ajith",
"Kent Yagi"
],
"categories": [
"gr-qc"
],
"license": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
"title": "Spacetime Quasi-normal Mode Oscillations of Anisotropic Neutron Stars",
"url": "https://arxiv.org/abs/2601.06962",
"version": "v1"
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