A Gravitational-Wave Perspective on Neutron-Star Seismology

Andersson, Nils

doi:10.3390/universe7040097

“…𝑓 -modes are some of the most efficient oscillations to emit GWs (McDermott et al 1988;Andersson & Kokkotas 1998) so we choose them as the modes we excite in our model. Furthermore, NS oscillations are of particular interest because, like with astroseismology or helioseismology, seismology of NSs can reveal information about the elusive interior (Andersson & Kokkotas 1998;Andersson 2021). The work presented here does not address the interesting question of how different interiors may affect our results, but this could (and should) be done at a later date.…”

Section: Introductionmentioning

confidence: 97%

Gravitational waves from small spin-up and spin-down events of neutron stars

Garvin¹,

Jones²

2022

Preprint

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Recently, Espinoza et al. (2014Espinoza et al. ( , 2021 reported the existence of "glitch candidates" and "anti-glitch candidates" which are effectively small spin-ups and spin-downs of a neutron star with magnitudes smaller than those seen in typical glitches. The physical origin of these small events is not yet understood. In this paper, we outline a model that can account for the changes in spin, and crucially, is independently testable with gravitational wave observations. In brief, the model posits that small spinup/spin-down events are caused by the excitation and decay of non-axisymmetric 𝑓 -modes which radiate angular momentum away in a burst-like way as gravitational waves. The model takes the change in spin frequency as an input and outputs the initial mode amplitude and the signal-to-noise ratio achievable from gravitational wave detectors. We find that the model presented here will become falsifiable once 3rd generation gravitational wave detectors, like the Einstein Telescope, begin taking data.

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“…The motivation for the glitch model comes from present f-mode GW searches by LIGO-VIRGO observations. While NS seismology (Andersson & Comer 2001;Kokkotas et al 2001;Andersson 2021) and the detectability (Abbott et al 2019b;Ho et al 2020;Abbott et al 2021Abbott et al , 2022aAbbott et al , 2022b of transient f-mode GW signal has been discussed, the assumption of f-mode excitation with an energy similar to that of typical pulsar glitches has been widely considered even though a clear explanation for the connection between the pulsar glitches and the mode excitation is yet to be found. By taking into account typical glitch energy and focusing on glitching pulsars, the problem becomes calculable and straightforward.…”

Section: Introductionmentioning

confidence: 99%

Constraining Nuclear Parameters Using Gravitational Waves from f-mode Oscillations in Neutron Stars

Pradhan,

Pathak,

Chatterjee

2023

ApJ

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Gravitational waves (GWs) emanating from unstable quasi-normal modes in neutron stars (NSs) could be accessible with the improved sensitivity of the current GW detectors or with the next-generation GW detectors and, therefore, can be employed to study the NS interior. Assuming f-mode excitation in isolated pulsars with typical energy of pulsar glitches and considering potential f-mode GW candidates for A+ (upgraded LIGO detectors operating at fifth observing run design sensitivity) and Einstein Telescope (ET), we demonstrate the inverse problem of NS asteroseismology within a Bayesian formalism to constrain the nuclear parameters and NS equation of state (EOS). We describe the NS interior within relativistic mean-field formalism. Taking the example of glitching pulsars, we find that for a single event in A+ and ET, among the nuclear parameters, the nucleon effective mass (m*) within 90% credible interval can be restricted within 10% and 5%, respectively. At the same time, the incompressibility (K) and the slope of the symmetry energy (L) are only loosely constrained. Considering multiple (10) events in A+ and ET, all the nuclear parameters are well constrained, especially m*, which can be constrained to 3% and 2% in A+ and ET, respectively. Uncertainty in the observables of a 1.4 M ⊙ NS such as radius ( R 1.4 M ⊙ ), f-mode frequency ( f 1.4 M ⊙ ), damping time ( τ 1.4 M ⊙ ), and a few EOS properties including squared speed of sound (c s 2) are also estimated.

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“…Searches for continuous GW sources potentially originating from these spinning neutron stars have been undertaken (Aasi et al 2015;Papa et al 2020;The LIGO Scientific Collaboration et al 2021c;Abbott et al 2022;The LIGO Scientific Collaboration et al 2022). From continuous GW searches, geophysical structure and seismology of neutron stars may be further probed (Geroyannis et al 2017;Yang et al 2018;Suvorov 2018;Andersson 2021).…”

Section: Introductionmentioning

confidence: 99%

Multi-messenger Emission from Tidal Waves in Neutron Star Oceans

Sullivan¹,

Alves²,

Spence³

et al. 2022

Preprint

0

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Astrophysical binary systems including neutron stars represent exciting sources for multimessenger astrophysics. A little considered source of electromagnetic transients accompanying compact binary systems is a neutron star ocean, the external fluid layer encasing a neutron star. We present a groundwork study into tidal waves in neutron star oceans and their consequences. Specifically, we investigate how oscillation modes in neutron star oceans can be tidally excited during compact binary inspirals and parabolic encounters to produce tidal waves. We find that neutron star oceans can sustain tidal waves with frequencies under 100 mHz. Our results suggest that resonant neutron star ocean tidal waves may serve as a never-before studied source for precursor electromagnetic emission prior to neutron star-black hole and binary neutron star mergers. Resonant neutron star ocean tidal waves, whose energy budget can reach 10 45 erg, may serve as very early warning signs (∼ 1 − 10 yr before merger) for compact binary mergers if accompanied by electromagnetic flares. Similarly, excited ocean tidal waves will coincide with neutron star parabolic encounters. Depending on the neutron star ocean model and a flare emission scenario, flares may be detectable by Fermi and NuSTAR out to ∼ 100 Mpc with detection rates as high as ∼ 7 yr −1 for binary neutron stars and ∼ 0.6 yr −1 for neutron star-black hole binaries. Observations of emission from neutron star ocean tidal waves along with gravitational waves will provide insight into the equation of state at the neutron star surface, the composition of neutron star oceans and crusts, and neutron star geophysics.

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A Gravitational-Wave Perspective on Neutron-Star Seismology

Cited by 32 publications

References 123 publications

Gravitational waves from small spin-up and spin-down events of neutron stars

Gravitational waves from small spin-up and spin-down events of neutron stars

Constraining Nuclear Parameters Using Gravitational Waves from f-mode Oscillations in Neutron Stars

Multi-messenger Emission from Tidal Waves in Neutron Star Oceans

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