On the formation history of Galactic double neutron stars

Abstract

Double neutron stars (DNSs) have been observed as Galactic radio pulsars, and the recent discovery of gravitational waves from the DNS merger GW170817 adds to the known DNS population. We perform rapid population synthesis of massive binary stars and discuss model predictions, including DNS formation rates, mass distributions, and delay time distributions. We vary assumptions and parameters of physical processes such as mass transfer stability criteria, supernova natal kick distributions, remnant mass prescriptions and common-envelope energetics. We compute the likelihood of observing the orbital period-eccentricity distribution of the Galactic DNS population under each of our population synthesis models, allowing us to quantitatively compare the models. We find that mass transfer from a stripped post-helium-burning secondary (case BB) onto a neutron star is most likely dynamically stable. We also find that a natal kick distribution composed of both low (Maxwellian σ = 30 km s −1 ) and high (σ = 265 km s −1 ) components is preferred over a single high-kick component. We conclude that the observed DNS mass distribution can place strong constraints on model assumptions.

Three-dimensional core-collapse supernova simulations of massive and rotating progenitors

“…These rather lower kick velocities are the result of the bipolar explosion geometry of both models (Figure 1). The low kick velocities have implications for the proposed correlation between explosion energy and kick velocity (Bray & Eldridge 2016;Janka 2017a;Vigna-Gómez et al 2018). Our results constitute further evidence that this correlation is not a tight one.…”

Modelling double neutron stars: radio and gravitational waves

“…This shows that the selection effects we have modelled are largely decoupled from the observed eccentricity distribution. It is clear by eye (and confirmed by the p-value) that our model does not provide a good match to the eccentricity distribution of Galactic DNSs (as shown before by Kiel et al 2010;Chruslinska et al 2017;Vigna-Gómez et al 2018). We believe there are two reasons for this discrepancy.…”

“…Stevenson et al 2017;Barrett et al 2018;Stevenson et al 2019;Bavera et al 2019) or a NS (e.g. Vigna-Gómez et al 2018;Neijssel et al 2019;Broekgaarden et al 2019), but did not follow any subsequent evolution of these objects. To analyse whether a NS is also a pulsar, other properties such as the magnetic field and spin period need to assigned to the NS and calculated over time, e.g.…”

“…Though the change is very slight, it emphasizes the importance of the pulsar parameters, even when comparing models to the orbital properties of Galactic DNSs (e.g. Andrews et al 2015;Vigna-Gómez et al 2018).…”

Dependence of gravitational wave transient rates on cosmic star formation and metallicity evolution history

“…Langer & Norman 2006;de Mink & Belczynski 2015;Eldridge et al 2019). There has been significant study of the how the uncertainties and assumptions in the stellar population models, especially the natalsupernova kick, affect the rate predictions and the observed double neutron star population (e.g Fryer et al 1998;Wex et al 2000;Dominik et al 2013;Lipunov & Pruzhinskaya ntan032@aucklanduni.ac.nz † j.eldridge@auckland.ac.nz 2014; Abbott et al 2016a;Tauris et al 2017;Belczynski et al 2017;Kruckow et al 2018;Vigna-Gómez et al 2018;Chruslinska et al 2018;Mapelli & Giacobbo 2018;Eldridge et al 2019;Andrews & Mandel 2019). However there are also substantial uncertainties in the star formation history of the Universe and its metallicity evolution which have been largely neglected until recently (Lamberts et al 2018;Chruslinska et al 2019;Mapelli et al 2019;Artale et al 2019;Neijssel et al 2019).…”