The long and the short of it: modelling double neutron star and collapsar Galactic dynamics

TL;DR

This study models the dynamics of double neutron stars and collapsars in the galaxy, revealing rapid mergers, the importance of common envelope evolution, and the spatial distribution differences compared to gamma-ray burst observations.

Contribution

It introduces a detailed population synthesis approach to analyze double compact binary systems and collapsars, highlighting key evolutionary phases and spatial distribution characteristics.

Findings

Double neutron star binaries can merge within a few million years.

Common envelope evolution is crucial in neutron star formation.

Projected gamma-ray burst distances are more centrally concentrated than model predictions.

Abstract

The work presented here examines populations of double compact binary systems and tidally enhanced collapsars. We make use of BINPOP and BINKIN, two components of a recently developed population synthesis package. Results focus on correlations of both binary and spatial evolutionary population characteristics. Pulsar and long duration gamma-ray burst observations are used in concert with our models to draw the conclusions that: double neutron star binaries can merge rapidly on timescales of a few million years (much less than that found for the observed double neutron star population), common envelope evolution within these models is a very important phase in double neutron star formation, and observations of long gamma-ray burst projected distances are more centrally concentrated than our simulated coalescing double neutron star and collapsar Galactic populations. Better agreement is found with dwarf galaxy models although the outcome is strongly linked to the assumed birth radial distribution. The birth rate of the double neutron star population in our models range from 4-160 Myr^-1 and the merger rate ranges from 3-150 Myr^-1. The upper and lower limits of the rates results from including electron capture supernova kicks to neutron stars and decreasing the common envelope efficiency respectively. Our double black hole merger rates suggest that black holes should receive an asymmetric kick at birth.