Prospects for distinguishing dynamical tides in inspiralling binary neutron stars with third generation gravitational-wave detectors

Abstract

Tidal effects in gravitational-wave (GW) observations from binary neutron star mergers have the potential to probe ultra-dense matter and shed light on the unknown nuclear equation of state of neutron stars. Tidal effects in inspiralling neutron star binaries become relevant at GW frequencies of a few hundred Hz and require detectors with exquisite high-frequency sensitivity. Third generation GW detectors such as the Einstein Telescope or Cosmic Explorer will be particularly sensitive in this high-frequency regime, allowing us to probe neutron star tides beyond the adiabatic approximation. Here we assess whether dynamical tides can be measured from a neutron star inspiral. We find that the measurability of dynamical tides depends strongly on the neutron star mass and equation of state. For a semi-realistic population of 10,000 inspiralling binary neutron stars, we conservatively estimate that on average $\mathcal{O}(50)$ binaries will have measurable dynamical tides. As dynamical tides are characterised not only by the star's tidal deformability but also by its fundamental ($f$-) mode frequency, they present a possibility of probing higher-order tidal effects and test consistency with quasi-universal relations. For a GW170817-like signal in a third generation detector network, we find that the stars' $f$-mode frequencies can be measured to within a few hundred Hz.