Comparing Compact Object Distributions from Mass- and Presupernova Core Structure-based Prescriptions

TL;DR

This study compares different methods for predicting compact object remnants in binary star populations, highlighting how core structure-based prescriptions differ from traditional mass-based methods in remnant mass predictions.

Contribution

It introduces and compares three methods for predicting remnant masses, emphasizing the importance of presupernova core structure over simple mass-based prescriptions.

Findings

Mass-based prescriptions predict more low-mass remnants and a wider neutron star mass range.

Core structure-based methods favor higher mass remnants and produce a narrower neutron star mass distribution.

Mass gap black holes are predicted only above 3.5 solar masses in structure-based models.

Abstract

Binary population synthesis (BPS) employs prescriptions to predict final fates, explosion or implosion, and remnant masses based on one or two stellar parameters at the evolutionary cutoff imposed by the code, usually at or near central carbon ignition. In doing this, BPS disregards the integral role late-stage evolution plays in determining the final fate, remnant type, and remnant mass within the neutrino-driven explosion paradigm. To highlight differences between a popular prescription which relies only on the core and final stellar mass and emerging methods which rely on a star's presupernova core structure, we generate a series of compact object distributions using three different methods for a sample population of single and binary stars computed in BPASS. The first method estimates remnant mass based on a star's carbon-oxygen (CO) core mass and final total mass. The second method uses the presupernova core structure based on the bare CO-core models of \citet{Pat20} combined with a parameterized explosion criterion to first determine final fate and remnant type, then remnant mass. The third method associates presupernova helium-core masses with remnant masses determined from public explosion models which rely implicitly on core structure. We find that the core-/final mass-based prescription favors lower mass remnants, including a large population of mass gap black holes, and predicts neutron star masses which span a wide range, whereas the structure-based prescriptions favor slightly higher mass remnants, mass gap black holes only as low as 3.5 \Msun, and predict neutron star mass distributions which cluster in a narrow range.