Detecting resonant tidal excitations of Rossby modes in coalescing neutron-star binaries with third-generation gravitational-wave detectors

TL;DR

This paper investigates how resonant tidal excitations of Rossby modes in neutron stars affect gravitational wave signals, enabling improved parameter estimation of neutron star properties with third-generation detectors.

Contribution

It introduces a new relation between r-mode overlap and tidal Love number and demonstrates how DT can significantly enhance neutron star parameter measurements.

Findings

R-mode dynamical tide can constrain neutron star spin frequencies to 6%.

Degeneracy in Love numbers is reduced by a factor of 300.

DT allows measurement of neutron star spin inclination angles to 0.09 radians.

Abstract

Rossby modes (r-modes) of rotating neutron stars can be excited by the gravitomagnetic forces in coalescing binary systems. The previous study by Flanagan and Racine [Phys. Rev. D 75, 044001 (2007)] showed that this kind of dynamical tide (DT) can induce phase shifts of 0.1 rad on gravitational waveforms, which is detectable by third-generation (3G) detectors. In this paper, we study the impact of this DT on measuring neutron-star parameters in the era of 3G detectors. We incorporate two universal relations among neutron star properties predicted by different equations of state: (i) the well-known I-Love relation between momentum of inertia and (f-mode) tidal Love number, and (ii) a relation between the r-mode overlap and tidal Love number, which is newly explored in this paper. We find that r-mode DT will provide rich information about slowly rotating neutron stars with frequency ranging from 10 to 100 Hz. For a binary neutron star system (with a signal-to-noise ratio around 1500 in the Cosmic Explorer), the spin frequency of each individual neutron star can be constrained to 6% (fractional error) in the best-case scenario. The degeneracy between the Love numbers of individual neutron stars is dramatically reduced: each individual Love number can be constrained to around 20% in the best case, while the fractional error for both symmetric and anti-symmetric Love numbers are reduced by factors of around 300. Furthermore, DT also allows us to measure the spin inclination angles of the neutron stars, to 0.09 rad in the best case, and thus place constraints on NS natal kicks and supernova explosion models. Besides parameter estimation, we have also developed a semi-analytic method that accurately describes detailed features of the binary evolution that arise due to the DT.