# Inspiralling eccentric binary neutron stars: orbital motion and tidal resonance

## TL;DR

This paper investigates the orbital dynamics and tidal resonances in eccentric binary neutron stars, revealing a significant phase shift in gravitational waves that could be detected by future detectors.

## Contribution

It introduces a model for eccentric binary neutron star orbits including tidal effects and identifies a novel orbital resonance affecting gravitational wave signals.

## Key findings

- Tidal interactions cause orbital precession beyond Post-Newtonian effects.
- A new orbital resonance at one third of the f-mode frequency is identified.
- Resonance can induce a detectable phase shift in gravitational waveforms.

## Abstract

We study the orbital evolution of eccentric binary neutron stars. The orbit is described as a Quasi-Keplarian orbit with perturbations due to tidal couplings. We find that the tidal interaction between stars contributes to orbital precession, in addition to the Post-Newtonian procession. The coupling between the angular and radial motion of the binary also excites a series of harmonics in the stars' oscillation. In the small eccentricity limit, this coupling mainly gives rise to an additional orbital resonance, with the orbital frequency being one third of the f-mode frequency. For a binary with initial eccentricity $\sim 0.2$ at $50$Hz orbital frequency, the presence of this tidal resonance introduces $\sim 0.5$ phase shift in the gravitational waveform till merger, subject to uncertainties in neutron star equation of state and the distribution of binary component masses. Such phase shift in the late-inspiral stage is likely detectable with third-generation gravitational-wave detectors.