Flame Evolution During Type Ia Supernovae and the Deflagration Phase in the Gravitationally Confined Detonation Scenario

Abstract

We develop an improved method for tracking the nuclear flame during the deflagration phase of a Type Ia supernova, and apply it to study the variation in outcomes expected from the gravitationally confined detonation (GCD) paradigm. A simplified 3-stage burning model and a non-static ash state are integrated with an artificially thickened advection-diffusion-reaction (ADR) flame front in order to provide an accurate but highly efficient representation of the energy release and electron capture in and after the unresolvable flame. We demonstrate that both our ADR and energy release methods do not generate significant acoustic noise, as has been a problem with previous ADR-based schemes. We proceed to model aspects of the deflagration, particularly the role of buoyancy of the hot ash, and find that our methods are reasonably well-behaved with respect to numerical resolution. We show that if a detonation occurs in material swept up by the material ejected by the first rising bubble but gravitationally confined to the white dwarf (WD) surface (the GCD paradigm), the density structure of the WD at detonation is systematically correlated with the distance of the deflagration ignition point from the center of the star. Coupled to a suitably stochastic ignition process, this correlation may provide a plausible explanation for the variety of nickel masses seen in Type Ia Supernovae.

STUDY OF THE DETONATION PHASE IN THE GRAVITATIONALLY CONFINED DETONATION MODEL OF TYPE Ia SUPERNOVAE

“…Additionally, energy losses (through neutrino emission) and changes in the electron mole fraction Y e due to weak interactions (electron and positron decays and captures) are incorporated by convolving the temperature-and density-dependent NSE distributions with all relevant weak reactions. Additional details concerning the nuclear physics and the numerical lookup scheme is presented in Calder et al (2007), Townsley et al (2007), and Seitenzahl et al (2009).…”

“…On the one hand, the conditions under which the thermonuclear runaway commences remain poorly understood so that the initial number and distribution of flamelets that seed the runaway is still a free parameter. On the other hand, although significant progress has been made in simulating flame fronts in multidimensional stellar models (see García-Senz & Bravo 2005;Gamezo et al 2005;Schmidt et al 2006b;Röpke et al 2007a;Townsley et al 2007;Jordan et al 2008, for recent examples from several groups), the challenge associated with modeling an unresolved turbulent deflagration (e.g., Schmidt et al 2006a) with limited computational resources injects an additional degree of uncertainty into the outcome of a model for any given choice of initial conditions. Readers are referred to Hillebrandt & Niemeyer (2000) for a review of the challenges associated with modeling and validating the SNe Ia explosion mechanism, and Röpke (2006) for an update on the state of multidimensional modeling.…”

“…We study the case of the gravitationally confined detonation (GCD) model of SNe Ia (Plewa et al 2004;Plewa 2007) for a single ignition point which is offset by a range of distances from the center of the star, as described in Townsley et al (2007). We follow the development of the explosion through the detonation phase and into homologous expansion.…”

Nucleosynthesis of Iron-Peak Elements in Type-Ia Supernovae

“…Both of us use level-set method to track the nuclear flame. But we have extended this idea to include a three-step burning [11]. The level-set method is responsible for carbon burning, and the NQSE and NSE are proceeded afterwards instead of instantaneous burning.…”

“…The laminar flame and detonation speed are taken from [9] and calculated using the scheme in [10]. The energy production by the explosion follows the three-step scheme as in [11], which includes carbon burning, nuclear quasi-statistical equilibrium (NQSE) burning and NSE burning. In NSE burning, electron capture is included.…”