Evolutionary Channels for the Formation of Double Neutron Stars

TL;DR

This study investigates the evolutionary pathways leading to double neutron star systems by analyzing binary models against observed systems, revealing key supernova mechanisms and formation channels.

Contribution

It identifies three main evolutionary channels for double neutron star formation and constrains binary evolution parameters using detailed system histories.

Findings

Less than half of models meet all observational constraints.

Electron-capture supernovae are crucial in forming these systems.

Most systems likely underwent Case BB mass transfer.

Abstract

We analyze binary population models of double-neutron stars and compare results to the accurately measured orbital periods and eccentricities of the eight known such systems in our Galaxy. In contrast to past similar studies, we especially focus on the dominant evolutionary channels (we identify three); for the first time, we use a detailed understanding of the evolutionary history of three double neutron stars as actual constraints on the population models. We find that the evolutionary constraints derived from the double pulsar are particularly tight, and less than half of the examined models survive the full set of constraints. The top-likelihood surviving models yield constraints on the key binary evolution parameters, but most interestingly reveal (i) the need for electron-capture supernovae from relatively low-mass degenerate, progenitor cores, and (ii) the most likely evolutionary paths for the rest of the known double neutron stars. In particular, we find that J1913+16 likely went through a phase of Case BB mass transfer, and J1906+0746 and J1756-2251 are consistent with having been formed in electron-capture supernovae.