Initial data for neutron star binaries with arbitrary spins

TL;DR

This paper introduces a new approximate method for generating initial data for binary neutron star simulations with arbitrary spins and eccentricities, demonstrating reduced eccentricity and realistic spin configurations.

Contribution

The authors develop a novel approximate initial data construction method for spinning neutron star binaries, improving initial eccentricity and spin realism in numerical relativity simulations.

Findings

Constraint violations decrease after a few orbits.

Simulations exhibit the orbital 'hang-up' effect.

Eccentricities are significantly lower than in previous models.

Abstract

The starting point of any general relativistic numerical simulation is a solution of the Hamiltonian and momentum constraints that (ideally) represents an astrophysically realistic scenario. We present a new method to produce initial data sets for binary neutron stars with arbitrary spins and orbital eccentricities. The method only provides approximate solutions to the constraints. However, we show that the corresponding constraint violations subside after a couple of orbits, becoming comparable to those found in evolutions of standard conformally flat, helically symmetric binary initial data. We evolve in time three data sets, corresponding to binaries with spins aligned, zero and anti-aligned with the orbital angular momentum. These simulations show the orbital "hang-up" effect previously seen in binary black holes. Additionally, all three show orbital eccentricities up to one order of magnitude smaller than those found in helically symmetric initial sets evolutions.