Heavy double neutron stars: birth, mid-life and death

TL;DR

This paper combines radio and gravitational-wave data to analyze the birth, evolution, and merger of double neutron-star systems, providing insights into their mass distribution and merger timescales.

Contribution

It introduces a model linking radio and gravitational-wave observations to better understand DNS evolution and suggests a significant fraction of fast-merging binaries.

Findings

GW190425 may belong to a fast-merging subpopulation.

Fast-merging binaries could constitute 8-79% of DNS at birth.

Delay times for fast mergers are estimated at 5-401 Myr.

Abstract

Radio pulsar observations probe the lives of Galactic double neutron-star (DNS) systems while gravitational waves enable us to study extragalactic DNS in their final moments. By combining measurements from radio and gravitational-wave astronomy, we seek to gain a more complete understanding of DNS from formation to merger. We analyse the recent gravitational-wave binary neutron star mergers GW170817 and GW190425 in the context of other DNS known from radio astronomy. By employing a model for the birth and evolution of DNS, we measure the mass distribution of DNS at birth, at mid-life (in the radio), and at death (in gravitational waves). We consider the hypothesis that the high-mass gravitational-wave event GW190425 is part of a subpopulation formed through unstable case BB mass transfer, which quickly merge in $\sim 10-100~\mathrm{Myr}$. We find mild evidence to support this hypothesis and that GW190425 is not a clear outlier from the radio population as previously claimed. If there are fast-merging binaries, we estimate that they constitute $8-79\%$ of DNS at birth (90% credibility). We estimate the typical delay time between the birth and death of fast-merging binaries to be $\approx 5-401~\mathrm{Myr}$ (90% credibility). We discuss the implications for radio and gravitational-wave astronomy.