A Three‐Dimensional Deflagration Model for Type Ia Supernovae Compared with Observations

Abstract

A simulation of the thermonuclear explosion of a Chandrasekhar-mass C+O white dwarf, the most popular scenario of a Type Ia supernova (SN Ia), is presented. The underlying modeling is pursued in a self-consistent way, treating the combustion wave as a turbulent deflagration using well tested methods developed for laboratory combustion and based on the concept of ''large-eddy simulations'' (LESs). Such consistency requires to capture the onset of the turbulent cascade on resolved scales. This is achieved by computing the dynamical evolution on a 1024 3 moving grid, which resulted in the best-resolved three-dimensional SN Ia simulation carried out thus far, reaching the limits of what can be done on present supercomputers. Consequently, the model has no free parameters other than the initial conditions at the onset of the explosion, and therefore it has considerable predictive power. Our main objective is to determine to which extent such a simulation can account for the observations of normal SNe Ia. Guided by previous simulations with less resolution and a less sophisticated flame model, initial conditions were chosen that yield a reasonably strong explosion and a sufficient amount of radioactive nickel for a bright display. We show that observables are indeed matched to a reasonable degree. In particular, good agreement is found with the light curves of normal SNe Ia. Moreover, the model reproduces the general features of the abundance stratification as inferred from the analysis of spectra. This indicates that it captures the main features of the explosion mechanism of SNe Ia. However, we also show that even a seemingly best-choice pure deflagration model has shortcomings that indicate the need for a different mode of nuclear burning at late times, perhaps the transition to a detonation at low density.

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

“…The initiation of the detonation takes place within the compressed gas which lies ahead of the high-velocity jet, and ahead of the internal shock which forms within the jet (see Section 4 and Figure 4). The focusing of the surface flow and the formation of the jet are also present in threedimensional simulations (Section 4; Jordan et al 2008;Röpke et al 2007a), and are therefore not an artifact of the twodimensional axisymmetric geometry used.…”

“…The progress of this eruption and flow is shown in Figure 1 for the case with r off = 40 km. As mentioned previously, there is indication from comparisons of recent work (Röpke et al 2007a;Townsley et al 2007;Jordan et al 2008) that the eruption pattern arising from a given offset is dependent on the choice of burning model, and therefore is currently uncertain. This has important consequences at the collision region because it sets the velocity and density structure of the incoming flows as well as the surface gravity (via the degree of stellar expansion) under which the collision occurs.…”

“…Detonation initiation through this process involves a complicated interplay between burning and hydrodynamic flow that requires a coherent build up of acoustic energy by the nuclear energy release. An often-cited criteria for the initiation of a detonation in the context of degenerate carbonoxygen material is that a "critical" mass of material needs to be heated and compressed above a certain temperature and density threshold (Arnett & Livne 1994;Niemeyer & Woosley 1997;Röpke et al 2007a). While these studies indicate the general conditions under which detonations might readily arise, thermodynamic conditions and heated masses alone represent Figure 8.…”

“…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.…”

Turbulence modeling and the physics of the intra-cluster medium

“…LES are customary, for example, in simulations of Type Ia supernovae [15,16,17,18,19]. Recently, [20] developed a similar tool designed for studying Rayleigh-Taylor driven turbulence in the interaction between AGN outflows and the ICM [21,22].…”