Effect of spin in binary neutron star mergers

TL;DR

This study explores how initial spin affects the dynamics, remnant properties, ejecta, gravitational waves, and neutrino emissions in binary neutron star mergers using relativistic hydrodynamics simulations.

Contribution

It provides the first detailed analysis of the impact of initial spin on various merger outcomes, including ejecta and remnant spins, with high-spin cases reaching record spins.

Findings

Highly aligned spins increase ejected mass up to 0.06 solar masses.

Remnants from high-spin mergers can reach a dimensionless spin of 0.92.

Initial spin significantly influences gravitational wave signals and neutrino emissions.

Abstract

We investigate the effect of spin on equal and unequal mass binary neutron star mergers using finite-temperature, composition-dependent Steiner-Fischer-Hempel equation of state with parameter set ``o'' (SFHo), via 3+1 general relativistic hydrodynamics simulations which take into account neutrino emission and absorption. Equal mass, irrotational cases that have a mass of $M_{1,2}$ =$1.27M_{\odot}$, result in a long-lived neutron star, while $1.52$ and $2.05M_{\odot}$ cases lead to a prompt collapse to a black hole. For all cases, we analyse the effect of initial spin on dynamics, on the structure of the final remnant, its spin evolution, the amount and composition of the ejected matter, gravitational waves, neutrino energies {and luminosities}, and disc masses. We show that in equal mass binary neutron star mergers, the ejected mass could reach $\sim0.06M_{\odot}$ for highly aligned-spins ($\chi=0.67$). The black hole which results from such a highly spinning, high-mass binary neutron star merger reaches a dimensionless spin of $0.92$; this is the highest spin reached in binary neutron star mergers, to date.