Anisotropic neutron star crust, solar system mountains, and gravitational waves

``Mountains'' or nonaxisymmetric deformations of rotating neutron stars (NS) efficiently radiate gravitational waves (GW). We consider analogies between NS mountains and surface features of solar system bodies. Both NS and moons such as Europa or Enceladus have thin crusts over deep oceans while Mercury has a thin crust over a large metallic core. Thin sheets may wrinkle in universal ways. Europa has linear features, Enceladus has ``tiger'' stripes, and Mercury has lobate scarps. NS may have analogous features. The innermost inner core of the Earth is anisotropic with a shear modulus that depends on direction. If NS crust material is also anisotropic this will produce an ellipticity, when the crust is stressed, that grows with spin frequency. This yields a braking index (log derivative of spin down rate assuming only GW spin down) very different from $n=5$ and could explain the maximum spin observed for neutron stars and a possible minimum ellipticity of millisecond pulsars.

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Publication Details

Journal
Physical review. D/Physical review. D.
Published
2024-08-05
DOI
https://doi.org/10.1103/physrevd.110.044016
Citations
6
Primary Topic
Pulsars and Gravitational Waves Research
Type
article
Field-Weighted Citation Impact
1.99

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article

Anisotropic neutron star crust, solar system mountains, and gravitational waves

J. A. Morales, C. J. Horowitz
6 citations
Physical review. D/Physical review. D.
Pulsars and Gravitational Waves Research
1.99
article

Anisotropic neutron star crust, solar system mountains, and gravitational waves

J. A. Morales, C. J. Horowitz
article en
6 citations

Abstract

``Mountains'' or nonaxisymmetric deformations of rotating neutron stars (NS) efficiently radiate gravitational waves (GW). We consider analogies between NS mountains and surface features of solar system bodies. Both NS and moons such as Europa or Enceladus have thin crusts over deep oceans while Mercury has a thin crust over a large metallic core. Thin sheets may wrinkle in universal ways. Europa has linear features, Enceladus has ``tiger'' stripes, and Mercury has lobate scarps. NS may have analogous features. The innermost inner core of the Earth is anisotropic with a shear modulus that depends on direction. If NS crust material is also anisotropic this will produce an ellipticity, when the crust is stressed, that grows with spin frequency. This yields a braking index (log derivative of spin down rate assuming only GW spin down) very different from $n=5$ and could explain the maximum spin observed for neutron stars and a possible minimum ellipticity of millisecond pulsars.

Physical review. D/Physical review. D.Vol. 110(4)
Indiana University Bloomington (US), Max Planck Institute for Gravitational Physics (DE), Michigan State University (US)
National Science Foundation, U.S. Department of Energy
Climate action
Openalex Percentile: Top 14%
Pulsars and Gravitational Waves Research
1.99
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