The One-Armed Spiral Instability in Neutron Star Mergers and its Detectability in Gravitational Waves

TL;DR

This study uses high-resolution simulations to analyze the one-armed spiral instability in neutron star merger remnants, revealing its potential gravitational wave signatures and assessing its detectability with current and future detectors.

Contribution

It demonstrates that the m=1 spiral instability is a common outcome in neutron star mergers and provides hybrid waveforms to evaluate its gravitational wave detectability.

Findings

The m=1 instability saturates within ~10 ms after merger.

Gravitational wave emission from the instability peaks at 1-2 kHz.

Detection of this instability requires third-generation detectors.

Abstract

We study the development and saturation of the $m=1$ one-armed spiral instability in remnants of binary neutron star mergers by means of high-resolution long-term numerical relativity simulations. Our results suggest that this instability is a generic outcome of neutron stars mergers in astrophysically relevant configurations; including both "stiff" and "soft" nuclear equations of state. We find that, once seeded at merger, the $m=1$ mode saturates within $\sim 10\ \mathrm{ms}$ and persists over secular timescales. Gravitational waves emitted by the $m=1$ instability have a peak frequency around $1-2\ \mathrm{kHz}$ and, if detected, could be used to constrain the equation of state of neutron stars. We construct hybrid waveforms spanning the entire Advanced LIGO band by combining our high-resolution numerical data with state-of-the-art effective-one-body waveforms including tidal effects. We use the complete hybrid waveforms to study the detectability of the one-armed spiral instability for both Advanced LIGO and the Einstein Telescope. We conclude that the one-armed spiral instability is not an efficient gravitational wave emitter. Its observation by current generation detectors is unlikely and will require third-generation interferometers.