Using gravitational-wave data to constrain dynamical tides in neutron star binaries

GW170817: Measurements of neutron star radii and equation of state The LIGO Scientific Collaboration and The Virgo Collaboration On August 17, 2017, the LIGO and Virgo observatories made the first direct detection of gravitational waves from the coalescence of a neutron star binary system. The detection of this gravitational wave signal, GW170817, offers a novel opportunity to directly probe the properties of matter at the extreme conditions found in the interior of these stars. The initial, minimal-assumption analysis of the LIGO and Virgo data placed constraints on the tidal effects of the coalescing bodies, which were then translated to constraints on neutron star radii. Here, we expand upon previous analyses by working under the hypothesis that both bodies were neutron stars that are described by the same equation of state and have spins within the range observed in Galactic binary neutron stars. Our analysis employs two methods: the use of equation-of-state-insensitive relations between various macroscopic properties of the neutron stars and the use of an efficient parameterization of the defining function p(ρ) of the equation of state itself. From the LIGO and Virgo data alone and the first method, we measure the two neutron star radii as R 1 = 10.8 +2.0 −1.7 km for the heavier star and R 2 = 10.7 +2.1 −1.5 km for the lighter star at the 90% credible level. If we additionally require that the equation of state supports neutron stars with masses larger than 1.97 M as required from electromagnetic observations and employ the equation of state parametrization, we further constrain R 1 = 11.9 +1.4 −1.4 km and R 2 = 11.9 +1.4 −1.4 km at the 90% credible level. Finally, we obtain constraints on p(ρ) at supranuclear densities, with pressure at twice nuclear saturation density measured at 3.5 +2.7 −1.7 × 10 34 dyn cm −2 at the 90% level.

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“…[42]). Finally, other stellar modes can couple to the tidal field and affect the GW signal [21,[43][44][45].…”

Section: Introductionmentioning

confidence: 99%

GW170817: Measurements of Neutron Star Radii and Equation of State

Abbott¹,

Abbott²,

Abbott³

et al. 2018

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“…The fastest spinning pulsar observed in BNS is PSR J0737-3039A, which spins at 44 Hz [49]. Andersson et al [50] estimated that it will spin down to 35 Hz as it enters the LIGO band. However, high spin rate is still physically allowed.…”

Section: Introductionmentioning

confidence: 99%

Excitation of f -modes during mergers of spinning binary neutron star

Chen

2020

Phys. Rev. D

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“…These mode pairs could provide a source of large nonlinear mode couplings for the two-superfluid version of the p − g instability discussed in recent papers (Weinberg et al 2013;Venumadhav et al 2014;Weinberg 2016). These instabilities may be observable through phase shifts in the gravitational waveforms of binary neutron star mergers (Essick et al 2016;Andersson & Ho 2018).…”

Section: P-modesmentioning

confidence: 99%

“…This would allow gravitational wave astronomy to serve as a probe of the equation of state above nuclear density, which is otherwise difficult to study. Low-frequency modes with frequencies swept by the orbital frequency may be resonantly excited by tidal interactions in neutron star-black hole and neutron star-neutron star mergers (Bildsten & Cutler 1992;Cutler et al 1993;Lai 1994;Reisenegger & Goldreich 1994;Xu & Lai 2017;Andersson & Ho 2018), causing a phase shift that depends on the exact nature of the excited modes. Low frequency g-modes are especially interesting, although the resulting gravitational waveform phase shifts from their resonant excitation will likely be impossible to measure with current-generation E-mail: pbr44@cornell.edu detectors unless the merging neutron stars are rapidly rotating or have large radii (Ho & Lai 1999;Flanagan & Racine 2007).…”

Section: Introductionmentioning

confidence: 99%

Compressional modes in two-superfluid neutron stars with leptonic buoyancy

Rau

Wasserman

2018

Monthly Notices of the Royal Astronomical Society

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We investigate the compressional modes of cold neutron stars with cores consisting of superfluid neutrons, superconducting protons and normal fluid electrons and muons, and crusts that contain superfluid neutrons plus a normal fluid of (spherical) nuclei and electrons. We develop a two-fluid formalism for the core that accounts for leptonic buoyancy, and an analogous treatment for the crust. We adopt the Cowling approximation, neglecting gravitational perturbations, but include all effects of the background space-time. We introduce a phenomenological, easily-modified nuclear equation of state which contains all of the thermodynamic information required to compute the coupled fluid oscillations, with parameters that are constrained by nuclear physics and the requirement that the maximum mass of a neutron star is ≥ 2M . Using four parametrizations of this equation of state with nuclear compressibilities K = 230-280 MeV, we calculate the Brunt-Väisälä frequency due to leptonic buoyancy, and find the corresponding g-mode frequencies and eigenfunctions. We find that the WKB approximation reproduces g-mode frequencies closely. We examine the dependence of g-mode frequencies on stellar mass, nuclear compressibility and strength of neutron-proton entrainment, and compare to previous calculations of g-mode frequencies due to leptonic buoyancy. We also compute the p-mode spectra, confirming previous findings that the two fluids behave as if uncoupled except the case of large entrainment, and show the existence of nearly resonant mode pairs which could lead to nonlinear p-g instabilities even at zero temperature.

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Using gravitational-wave data to constrain dynamical tides in neutron star binaries

Cited by 41 publications

References 74 publications

GW170817: Measurements of Neutron Star Radii and Equation of State

GW170817: Measurements of Neutron Star Radii and Equation of State

Excitation of f -modes during mergers of spinning binary neutron star

Compressional modes in two-superfluid neutron stars with leptonic buoyancy

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