Resonant tidal excitation of superfluid neutron stars in coalescing binaries

• Published in: Monthly notices of the Royal Astronomical Society 2017-01, Vol.464 (3), p.2622-2622
• Main Authors: Yu, Hang, Weinberg, Nevin N
• Format: Article
• Language: English
• Subjects: Buoyancy; Computational fluid dynamics; Detectors; Excitation; Fluids; Neutron stars; Phase error; Star & galaxy formation; Superfluidity
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stw2552

We study the resonant tidal excitation of g modes in coalescing superfluid neutron star (NS) binaries and investigate how such tidal driving impacts the gravitational-wave (GW) signal of the inspiral. Previous studies of this type treated the NS core as a normal fluid and thus did not account for its expected superfluidity. The source of buoyancy that supports the g modes is fundamentally different in the two cases: in a normal fluid core, the buoyancy is due to gradients in the proton-to-neutron fraction, whereas in a superfluid core it is due to gradients in the muon-to-electron fraction. The latter yields a stronger stratification and a superfluid NS therefore has a denser spectrum of g modes with frequencies above 10 Hz. As a result, many more g modes undergo resonant tidal excitation as the binary sweeps through the bandwidth of GW detectors such as LIGO. We find that ... 10 times more orbital energy is transferred into g-mode oscillations if the NS has a superfluid core rather than a normal fluid core. However, because this energy is transferred later in the inspiral when the orbital decay is faster, the accumulated phase error in the gravitational waveform is comparable for a superfluid and a normal fluid NS (~10 super( -3)-10 super( -2)rad). A phase error of this magnitude is too small to be measured from a single event with the current generation of GW detectors. (ProQuest: ... denotes formulae/symbols omitted.)