The formation of single neutron stars from double white-dwarf mergers via accretion-induced collapse

Abstract

The merging of double white-dwarfs (WDs) may produce the events of accretion-induced collapse (AIC) and form single neutron stars (NSs). Meanwhile, it is also notable that the recently proposed WD+He subgiant scenario has a significant contribution to the production of massive double WDs, in which the primary WD grows in mass by accreting He-rich material from a He subgiant companion. In this work, we aim to study the binary population synthesis (BPS) properties of AIC events from the double WD mergers by considering the classical scenarios and also the contribution of the WD+He subgiant scenario to the formation of double WDs. Firstly, we provided a dense and large model grid of WD+He star systems for producing AIC events through the double WD merger scenario. Secondly, we performed several sets of BPS calculations to obtain the rates and single NS number in our Galaxy. We found that the rates of AIC events from the double WD mergers in the Galaxy are in the range of 1.4−8.9×10 −3 yr −1 for all ONe/CO WD+ONe/CO WD mergers, and in the range of 0.3−3.8 × 10 −3 yr −1 when double CO WD mergers are not considered. We also found that the number of single NSs from AIC events in our Galaxy are in the range of 0.1−5.9 × 10 6 . The chirp mass of double WDs for producing AIC events distribute in the range of 0.55−1.25 M ⊙ . We estimated that more than half of double WDs for producing AIC events are capable to be observed by the future space-based gravitational wave detectors.

The formation of neutron star systems through accretion-induced collapse in white-dwarf binaries

“…In Scenario C, the double WDs can be also formed after the first CE ejection directly in some cases. Among the three scenarios, AIC events are mainly produced by Scenarios A and B, in which each scenario contributes to about 40% AIC events (see Liu & Wang 2020). For more discussions on the formation of double CO WDs, see previous studies (e.g., Han 1998;Nelemans et al 2001a;Ruiter et al 2009Ruiter et al , 2013Toonen et al 2012;Yungelson & Kuranov 2017).…”

“…4.3) and contain important information for the constraints on the CE evolution (e.g., Han 1998;Nelemans et al 2001a). In the double-degenerate model of AIC events, a WD merges with another WD in a compact binary with the total mass heavier than M Ch , the merging of which results from the GW radiation that causes its orbit to shrink, forming an AIC event finally (e.g., Lyutikov & Toonen 2017;Ruiter et al 2019;Liu & Wang 2020). The double-degenerate model mainly involves the merger of double CO WDs (the double CO WD channel), the merger of double ONe WDs (the double ONe WD channel), and the merger of ONe WD+CO WD systems (the ONe WD+CO WD channel).…”

“…Kashyap et al (2018) recently argued that the mergers of ONe WD+CO WD systems might also form the very faint and rapidly fading SNe Ia through a failed detonation. Liu & Wang (2020) recently studied the formation of AIC events through the merging of different kinds of double WDs in a systematic way. For more studies on the double-degenerate model of AIC events, see, e.g., Lyutikov & Toonen (2017) and Ruiter et al (2019).…”

“…According to the evolutionary stage of the primordial primary when it first fills its Roche-lobe, there are three evolutionary scenarios to form ONe WD+CO WD systems and then merge to produce AIC events (see Fig. 10), in which Scenario A is the main way to form AIC events (see Liu & Wang 2020). In Fig.…”

“…( 2) The double-degenerate model. In this model, an AIC event results from the merging of double WDs with a total mass heavier than M Ch (e.g., Nomoto & Iben 1985;Saio & Nomoto 1985;Ruiter et al 2019;Liu & Wang 2020). The singledegenerate model mainly produces NS binary systems, whereas the outcomes of the double-degenerate model are single isolated NSs.…”