Spacetime Quasi-normal Mode Oscillations of Anisotropic Neutron Stars
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arXiv
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| Autores principales: | , , , , |
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| Formato: | Preprint |
| Publicado: |
2026
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| _version_ | 1866911368197701632 |
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| author | Yu, Jihao Guedes, Victor Lau, Shu Yan Ajith, Siddarth Yagi, Kent |
| author_facet | Yu, Jihao Guedes, Victor Lau, Shu Yan Ajith, Siddarth Yagi, Kent |
| contents | 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. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2601_06962 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Spacetime Quasi-normal Mode Oscillations of Anisotropic Neutron Stars Yu, Jihao Guedes, Victor Lau, Shu Yan Ajith, Siddarth Yagi, Kent General Relativity and Quantum Cosmology 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. |
| title | Spacetime Quasi-normal Mode Oscillations of Anisotropic Neutron Stars |
| topic | General Relativity and Quantum Cosmology |
| url | https://arxiv.org/abs/2601.06962 |