2026MNRAS.545f2009K

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', via 3 + 1 general relativistic hydrodynamics simulations, which take into account neutrino emission and absorption. Equal-mass, irrotational cases that have a mass of $M_{1,2}$ = $1.27\ {\rm M}_{\odot }$ result in a long-lived neutron star, while 1.52 and $2.05\ {\rm M}_{\odot }$ 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 ${\sim}0.06\ {\rm M}_{\odot }$ for highly aligned spins ($\chi =0.67$). The black hole that 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.