Neutron star spin-kick velocity correlation effect on binary neutron star coalescence rates and spin-orbit misalignment of the components

TL;DR

This paper investigates how the alignment between neutron star spins and kick velocities affects the rate of binary neutron star mergers and their spin-orbit misalignments, revealing significant impacts especially with strong alignments.

Contribution

It introduces models considering spin-kick alignment effects on binary neutron star coalescence rates and spin-orbit misalignments, highlighting the importance of these correlations.

Findings

Strong spin-kick alignment reduces merger rates.

Alignment narrows spin-orbit misalignment distributions.

Large kicks with alignment significantly impact coalescence predictions.

Abstract

We study the effect of the neutron star spin -- kick velocity alignment observed in young radio pulsars on the coalescence rate of binary neutron stars. Two scenarios of the neutron star formation are considered: when the kick is always present and when it is small or absent if a neutron star is formed in a binary system due to electron-capture degenerate core collapse. The effect is shown to be especially strong for large kick amplitudes and tight alignments, reducing the expected galactic rate of binary neutron star coalescences compared to calculations with randomly directed kicks. The spin-kick correlation also leads to a much narrower NS spin-orbit misalignment.