Do electron-capture supernovae make neutron stars?

Abstract

Context. In the classical picture, electron-capture supernovae and the accretion-induced collapse of oxygen-neon white dwarfs undergo an oxygen deflagration phase before gravitational collapse produces a neutron star. These types of core collapse events are postulated to explain several astronomical phenomena. In this work, the oxygen deflagration phase is simulated for the first time using multidimensional hydrodynamics. Aims. By simulating the oxygen deflagration with multidimensional hydrodynamics and a level-set-based flame approach, new insights can be gained into the explosive deaths of 8−10 M stars and oxygen-neon white dwarfs that accrete material from a binary companion star. The main aim is to determine whether these events are thermonuclear or core-collapse supernova explosions, and hence whether neutron stars are formed by such phenomena. Methods. The oxygen deflagration is simulated in oxygen-neon cores with three different central ignition densities. The intermediate density case is perhaps the most realistic, being based on recent nuclear physics calculations and 1D stellar models. The 3D hydrodynamic simulations presented in this work begin from a centrally confined flame structure using a level-set-based flame approach and are performed in 256 3 and 512 3 numerical resolutions. Results. In the simulations with intermediate and low ignition density, the cores do not appear to collapse into neutron stars. Instead, almost a solar mass of material becomes unbound from the cores, leaving bound remnants. These simulations represent the case in which semiconvective mixing during the electron-capture phase preceding the deflagration is inefficient. The masses of the bound remnants double when Coulomb corrections are included in the equation of state, however they still do not exceed the effective Chandrasekhar mass and, hence, would not collapse into neutron stars. The simulations with the highest ignition density (log 10 ρ c = 10.3), representing the case where semiconvective mixing is very efficient, show clear signs that the core will collapse into a neutron star.

Fast and Luminous Transients from the Explosions of Long-lived Massive White Dwarf Merger Remnants

“…The light curve will look different from that of canonical AIC (Woosley & Baron 1992;Piro & Kulkarni 2013) or a strippedenvelope electron capture supernova (Moriya & Eldridge 2016), since the envelopes in our models extend out to ∼ a few×100R , and thus produce much brighter light curves. They also look different from regular electroncapture SNe from 8 − 10M stars, due to the much smaller envelope masses, producing shorter light curves that lack hydrogen (Takahashi et al 2013;Smith 2013;Tauris et al 2015;Jones et al 2016 …”

Type Ia supernovae from non-accreting progenitors

“…Hence, the deflagration ashes will likely be buoyant, leading to expansion, which will in turn limit the deleptonization rate. This hypothesis is strongly supported by 3D hydrodynamic simula- tions of ECSN deflagrations by Jones et al (2016Jones et al ( , 2019: their least compact progenitor ingites at log 10 (ρ c /g cm −3 ) = 9.90 but still manages to eject ∼ 1 M of material. Similarly, Marquardt et al (2015) simulate ONe WD detonations at lower densities and demonstrate that the explosion is practically identical to a typical SN Ia.…”

“…In this case, oxygen ignites above log 10 (ρ c /g cm −3 ) 10 and only after 20 Ne electron captures have started to occur at a significant rate. Hence, in the absence of residual carbon, this star would produce a core-collapse or a thermonuclear ECSN (Jones et al 2016).…”

“…However, recent three-dimensional hydrodynamical simulations of oxygen deflagrations in ONe cores at central densities ≥ 10 10 g cm −3 , viz. after the onset of electron-captures on 20 Ne, suggest that a large fraction of the star (≥ 1 M ) may be ejected in a so-called thermonuclear ECSN, leaving behind only a small bound remnant (Jones et al 2016(Jones et al , 2019.…”

Key issues review: numerical studies of turbulence in stars

“…Extension of simulations to investigation of the boundary between core collapse and thermonuclear explosion of ONe cores (Jones et al 2016), and to the white dwarf merger channel for SNIa and merger in general and common envelope evolution ) is beginning to be made. The resolution issue seems particularly acute for mergers because of the steep gradient at the surface of each star (a boundary problem).…”