# General-Relativistic Large-Eddy Simulations of Binary Neutron Star Mergers

## TL;DR

This paper introduces a new general-relativistic large-eddy simulation method to model turbulence in binary neutron star mergers, revealing its impact on remnant structure, emissions, and gravitational-wave signals, with implications for astrophysical observations.

## Contribution

It develops the first large-eddy simulation formalism for turbulence in general relativity applied to neutron star mergers, enhancing understanding of turbulence effects on merger outcomes.

## Key findings

- Turbulence influences remnant structure and lifetime.
- Gravitational-wave signals are only weakly affected by turbulence.
- Post-merger GW models are validated by the simulations.

## Abstract

The flow inside remnants of binary neutron star (NS) mergers is expected to be turbulent, because of magnetohydrodynamics instability activated at scales too small to be resolved in simulations. To study the large-scale impact of these instabilities, we develop a new formalism, based on the large-eddy simulation technique, for the modeling of subgrid-scale turbulent transport in general relativity. We apply it, for the first time, to the simulation of the late-inspiral and merger of two NSs. We find that turbulence can significantly affect the structure and survival time of the merger remnant, as well as its gravitational-wave (GW) and neutrino emissions. The former will be relevant for GW observation of merging neutron stars. The latter will affect the composition of the outflow driven by the merger and might influence its nucleosynthetic yields. The accretion rate after black-hole formation is also affected. Nevertheless, we find that, for the most likely values of the turbulence mixing efficiency, these effects are relatively small and the GW signal will be affected only weakly by the turbulence. Thus, our simulations provide a first validation of all existing post-merger GW models.