Impact of extreme spins and mass ratios on the post-merger observables of high-mass binary neutron stars

TL;DR

This study investigates how extreme spins and mass ratios in high-mass binary neutron star mergers influence post-merger observables, revealing significant effects on ejecta, remnant lifetime, and kilonova signals, which can help interpret gravitational-wave data.

Contribution

The paper presents the first systematic numerical-relativity simulations of high-mass, highly spinning binary neutron star mergers with large mass asymmetries, highlighting their impact on observable signatures.

Findings

High spins significantly alter remnant lifetime and ejecta properties.

Mass asymmetries combined with high spins affect kilonova brightness and duration.

Differences in observables can help distinguish spin and mass ratio effects in gravitational-wave signals.

Abstract

The gravitational-wave events GW170817 and GW190425 have led to a number of important insights on the equation of state of dense matter and the properties of neutron stars, such as their radii and the maximum mass. Some of these conclusions have been drawn on the basis of numerical-relativity simulations of binary neutron-star mergers with vanishing initial spins. While this may be a reasonable assumption in equal-mass systems, it may be violated in the presence of large mass asymmetries accompanied by the presence of high spins. To quantify the impact of high spins on multi-messenger gravitational-wave events, we have carried out a series of high-mass binary neutron-star mergers with a highly spinning primary star and large mass asymmetries that have been modelled self-consistently using two temperature-dependent equations of state. We show that, when compared with equal-mass, irrotational binaries, these systems can lead to significant differences in the remnant lifetime, in the dynamical ejecta, in the remnant disc masses, in the secular ejecta, and on the bulk kilonova properties. These differences could be exploited to remove the degeneracy between low- and high-spin priors in the detection of gravitational waves from binary neutron-star mergers.