Constructing Binary Neutron Star Initial Data with High Spins, High Compactness, and High Mass-Ratios

TL;DR

This paper presents an upgraded pseudospectral code for generating initial data of binary neutron star systems, enabling simulations of more extreme and diverse configurations to improve gravitational wave modeling.

Contribution

The authors introduce a new version of the SGRID code that allows for the simulation of binary neutron stars with high spins, compactness, and mass ratios beyond previous limits.

Findings

Successfully simulated neutron stars near breakup spin

Modeled highly compact neutron stars at 98% maximum mass

Simulated unequal mass systems with q=2.03

Abstract

The construction of accurate and consistent initial data for various binary parameters is a critical ingredient for numerical relativity simulations of the compact binary coalescence. In this article, we present an upgrade of the pseudospectral SGRID code, which enables us to access even larger regions of the binary neutron star parameter space. As a proof of principle, we present a selected set of first simulations based on initial configurations computed with the new code version. In particular, we simulate two millisecond pulsars close to their breakup spin, highly compact neutron stars with masses at about $98\%$ of the maximum supported mass of the employed equation of state, and an unequal mass systems with mass ratios even outside the range predicted by population synthesis models ($q = 2.03$). The discussed code extension will help us to simulate previously unexplored binary configurations. This is a necessary step to construct and test new gravitational wave approximants and to interpret upcoming binary neutron star merger observations. When we construct initial data, one has to specify various parameters, such as a rotation parameter for each star. Some of these parameters do not have direct physical meaning, which makes comparisons with other methods or models difficult. To facilitate this, we introduce simple estimates for the initial spin, momentum, mass, and center of mass of each individual star.