Nuclear Dominated Accretion Flows in Two Dimensions. I. Torus Evolution With Parametric Microphysics

Abstract

We explore the evolution of radiatively inefficient accretion disks in which nuclear reactions are dynamically important ("Nuclear Dominated Accretion Flows" or NuDAFs). Examples of such disks are those generated by the merger of a white dwarf with a neutron star or black hole, or by the collapse of a rotating star. Here, we present two-dimensional hydrodynamic simulations that systematically explore the effect of adding a single nuclear reaction to a viscous torus. The equation of state, anomalous shear stress, and nuclear reactions are given parametric forms. Our results point to the existence of two qualitatively different regimes of NuDAF evolution: (1) steady accretion with quiescent burning or (2) detonation of the disk. These outcomes are controlled primarily by the ratio Ψ of the nuclear energy released to the enthalpy at the burning radius. Disks detonate if Ψ exceeds a critical value Ψ crit ∼ 1, and if burning occurs in regions where neutrino cooling is unimportant. Thermonuclear runaways are seeded by the turbulent mixing of hot ash with cold fuel at the burning front. Disks with Ψ < Ψ crit do not explode, but instead power a persistent collimated outflow of unbound material composed primarily of ash, with a mass-loss rate that increases with Ψ. We discuss the implications of our results for supernova-like counterparts from astrophysical events in the NuDAF regime. In particular, detonations following a white dwarf-neutron star merger could account for some subluminous Type Ia supernovae, such as the class defined by SN 2002cx.

THE ROLE OF FISSION IN NEUTRON STAR MERGERS AND ITS IMPACT ON THEr-PROCESS PEAKS

“…Here we utilized only the conditions for the dynamical ejecta of NSM within the treatment of Korobkin et al (2012) or Bauswein et al (2013). However, these dynamical ejecta can also be affected by neutrino interactions and NSM ejecta also include, apart from the dynamical channel, matter ejected via neutrino-driven winds (e.g., Dessart et al 2009;Just et al 2014;Perego et al 2014;Rosswog et al 2014) and matter from unbinding a substantial fraction of the late-time accretion disk (e.g., Beloborodov 2008;Metzger et al 2008;Lee et al 2009;Fernández & Metzger 2013a, 2013bJust et al 2014). These additional channels yield larger electron fractions, since matter stays substantially longer near the hot central remnant and therefore positron captures and neutrino absorptions are likely.…”

Faint rapid red transients from neutron star–CO white dwarf mergers

“…Mergers of neutron stars (NSs) or black holes (BH) with white dwarfs (WDs) have been explored through several hydrodynamical and nuclear-hydrodynamical simulations, e.g. Fernández & Metzger (2013a); Bobrick et al (2017); Zenati et al (2019); Fernández et al (2019). All CO WD-NS mergers are expected to lead to unstable mass transfer (Bobrick et al 2017) where the WD is tidally disrupted on dynamical timescales and forms an extended debris disk around the NS (Papaloizou & Pringle 1984;Fryer et al 1999).…”

Merger of a white dwarf–neutron star binary to 1029carat diamonds: origin of the pulsar planets

“…The early phases of a WD-NS merger have been previously studied as sources of gamma-ray bursts (Fryer et al 1999;King et al 2007;Paschalidis et al 2011) and SNlike optical transients (Metzger 2012;Fernández & Metzger 2013;MM16). The stages in the evolution of such systems are briefly summarized as follows (e.g.…”