Modelling neutron star mountains

Gittins, Fabian; Andersson, Nils; Jones, D. I.

doi:10.1093/mnras/staa3635

Cited by 53 publications

(49 citation statements)

References 100 publications

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“…In concordance with previous work (e. g., Gittins et al 2021 and references therein), we find this theoretical upper limit to be much higher than observational constraints for millisecond pulsars, 10 −8 from the non-detection of gravitational waves (Abbott et al 2020) and in some cases as low as 10 −9 from the small measured slow-down of their rotation (e. g., Woan et al 2018). Thus, we confirm that the strength of their crust could allow millisecond pulsars to be much less axially symmetric than observed.…”

Section: Ellipticity and Gravitational Wave Emissionsupporting

confidence: 93%

Revisiting neutron starquakes caused by spin-down

Rencoret,

Aguilera-Gómez,

Reisenegger

2021

Preprint

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Context. Pulsars show a steady decrease in their rotational frequency, occasionally interrupted by sudden spin-ups called glitches, whose physical origin is still a mystery. One suggested explanation for at least the small glitches are starquakes, i. e., failures of the solid neutron star crust, in which the progressive reduction of the centrifugal force deforms the star, stressing the solid until it breaks. This produces a spin-up, dissipating energy inside the star. Aims. We explore this suggestion by analyzing a mostly analytical model in order to understand the possible consequences of starquakes, particularly whether they can explain at least the small glitches. Methods. We analyze the deformations and strains produced by the decreasing centrifugal force, modeling the neutron star with a fluid core and a solid crust, each with uniform density and with the core possibly denser than the crust. Results. The deformation of a star with very different densities in the core and crust is qualitatively different from the previously studied case of equal densities. The former more closely resembles the behaviour of a fluid star, in which the core-crust interface is a surface of constant gravitational plus centrifugal potential. Conclusions. Regardless of the uncertain breaking strain, the glitch activity in this model is several orders of magnitude smaller than observed, even if only small glitches are considered. For a large breaking strain, suggested by simulations, glitches due to starquakes could be roughly of the correct size, but much less frequent than observed glitches. The energy released in each such glitch is much larger than in the standard model of angular momentum transfer from a faster rotating superfluid in the inner crust. We also confirm that stresses in the neutron star crust can in principle support an ellipticity much larger than some observational upper limits from pulsar timing and continuous gravitational wave searches.

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Section: Ellipticity and Gravitational Wave Emissionsupporting

confidence: 93%

Revisiting neutron starquakes caused by spin-down

Rencoret,

Aguilera-Gómez,

Reisenegger

2021

Preprint

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“…We see that the models begin to result in similar estimates near N ∼ 10 6 above 10 −6 . This may be the maximum allowed by the NS's crust (Ushomirsky et al 2000;Horowitz & Kadau 2009;Gittins et al 2020), which is only slightly disfavored by our results. We predict that only 10 5 , or 0.1%, of Galactic NSs have been probed above = 10 −5.5 .…”

Section: Discussionmentioning

confidence: 43%

“…We expect a distribution of ellipticities across Galactic NSs. The maximum allowed ellipticity may be limited by the breaking strain of the NS crust to few × 10 −6 (Ushomirsky et al 2000;Horowitz & Kadau 2009;Gittins et al 2020). In order for a NS to support a larger , there may need to be an exotic solid phase in the core, such as crystalline quark matter (Owen 2005;Johnson-McDaniel & Owen 2013).…”

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confidence: 99%

Modeling the Galactic Neutron Star Population for Use in Continuous Gravitational Wave Searches

Reed,

Deibel,

Horowitz

2021

Preprint

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Searches for continuous gravitational waves from unknown Galactic neutron stars provide limits on the shapes of neutron stars. A rotating neutron star will produce gravitational waves if asymmetric deformations exist in its structure that are characterized by the star's ellipticity. In this study, we use a simple model of the spatial and spin distribution of Galactic neutron stars to estimate the total number of neutron stars probed, using gravitational waves, to a given upper limit on the ellipticity. This may help optimize future searches with improved sensitivity. The improved sensitivity of third-generation gravitational wave detectors may increase the number of neutron stars probed, to a given ellipticity, by factors of 100 to 1000.

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“…While this limit is much higher than those of old recycled millisecond pulsars (for which ε < 10 −8 ; Abbott et al 2020), young pulsars such as PSR J0537−6910 and the Crab pulsar are important because they have much stronger magnetic fields (and are hotter) and thus might have greater ellipticities. The ellipticity constraint of PSR J0537−6910 is also above or near estimates of the maximum ellipticity that can be sustained by an elastically deformed neutron star crust (Johnson-McDaniel & Owen 2013;Caplan et al 2018;Gittins et al 2021).…”

Section: Discussionmentioning

confidence: 75%

Diving below the Spin-down Limit: Constraints on Gravitational Waves from the Energetic Young Pulsar PSR J0537-6910

Abbott

Abraham

et al. 2021

ApJL

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We present a search for quasi-monochromatic gravitational-wave signals from the young, energetic X-ray pulsar PSR J0537−6910 using data from the second and third observing runs of LIGO and Virgo. The search is enabled by a contemporaneous timing ephemeris obtained using Neutron star Interior Composition Explorer (NICER) data. The NICER ephemeris has also been extended through 2020 October and includes three new glitches. PSR J0537 −6910 has the largest spin-down luminosity of any pulsar and exhibits fRequent and strong glitches. Analyses of its long-term and interglitch braking indices provide intriguing evidence that its spin-down energy budget may include gravitational-wave emission from a time-varying mass quadrupole moment. Its 62 Hz rotation frequency also puts its possible gravitational-wave emission in the most sensitive band of the LIGO/Virgo detectors. Motivated by these considerations, we search for gravitational-wave emission at both once and twice the rotation frequency from PSR J0537−6910. We find no signal, however, and report upper limits. Assuming a rigidly rotating triaxial star, our constraints reach below the gravitational-wave spin-down limit for this star for the first time by more than a factor of 2 and limit gravitational waves from the l = m = 2 mode to account for less than 14% of the spin-down energy budget. The fiducial equatorial ellipticity is constrained to less than about 3 ×10 −5 , which is the third best constraint for any young pulsar.

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Modelling neutron star mountains

Cited by 53 publications

References 100 publications

Revisiting neutron starquakes caused by spin-down

Revisiting neutron starquakes caused by spin-down

Modeling the Galactic Neutron Star Population for Use in Continuous Gravitational Wave Searches

Diving below the Spin-down Limit: Constraints on Gravitational Waves from the Energetic Young Pulsar PSR J0537-6910

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