Modeling the outcome of supernova explosions in binary population synthesis using the stellar compactness

TL;DR

This paper introduces a new supernova model based on stellar compactness within a binary population synthesis framework, revealing how core properties influence black hole and neutron star formation and the resulting gravitational-wave sources.

Contribution

The paper implements a compactness-based supernova model in MOBSE, providing new insights into binary compact object formation and the mass gap in black holes and neutron stars.

Findings

Formation rates of compact binaries depend on the compactness threshold.

The upper edge of the black hole-neutron star mass gap is influenced by fallback fraction.

Compactness signatures affect the population characteristics of merging binaries.

Abstract

Following the collapse of their cores, some of the massive binary stars that populate our Universe are expected to form merging binaries composed of black holes and neutron stars. Gravitational-wave observations of the resulting compact binaries can reveal precious details on the inner workings of the supernova mechanism and the subsequent formation of compact objects. Within the framework of the population-synthesis code MOBSE, we present the implementation of a new supernova model that relies on the compactness of the collapsing star. The model has two free parameters, namely the compactness threshold that separates the formation of black holes and that of neutron stars, and the fraction of the envelope that falls back onto the newly formed black holes. We compare this model extensively against other prescriptions that are commonly used in binary population synthesis. We find that the cleanest signatures of the role of the pre-supernova stellar compactness are (i) the relative formation rates of the different kinds of compact binaries, which mainly depend on the compactness threshold parameter, and (ii) the location of the upper edge of the mass gap between the lightest black holes and the heaviest neutron stars, which mainly depends on the fallback fraction.