Modeling the Diversity of Type Ia Supernova Explosions (original) (raw)

On Simulating Type Ia Supernovae

Journal of Physics: Conference Series, 2012

Type Ia supernovae are bright stellar explosions distinguished by standardizable light curves that allow for their use as distance indicators for cosmological studies. Despite their highly successful use in this capacity, the progenitors of these events are incompletely understood. We describe simulating type Ia supernovae in the paradigm of a thermonuclear runaway occurring in a massive white dwarf star. We describe the multi-scale physical processes that realistic models must incorporate and the numerical models for these that we employ. In particular, we describe a flame-capturing scheme that addresses the problem of turbulent thermonuclear combustion on unresolved scales. We present the results of our study of the systematics of type Ia supernovae including trends in brightness following from properties of the host galaxy that agree with observations. We also present performance results from simulations on leadership-class architectures.

Type Ia supernovae: Advances in large scale simulation

Journal of Physics: Conference Series, 2009

Using the newly developed petascale codes, MAESTRO and CASTRO, the Computational Astrophysics Consortium is simulating the explosion of white dwarf stars as Type Ia supernovae. Since the outcome is sensitive to where the nuclear runaway ignites, three sorts of calculations are being carried out. In the first, the presupernova convection of rotating and non-rotating white dwarfs is followed for several hours (star time), using MAESTRO, in order to determine just where the first sparks ignite. The turbulent nuclear combustion of the explosion is then followed using the compressible hydro code CASTRO in two other studies that assume either central or off-center ignition. Current calculations are running on 4000 -12000 CPU, but larger studies, on a greater number of CPU, will be required to increase the Reynolds number of the ignition study and the fidelity of the turbulence in the explosion studies.

Numerical Modeling of Type Ia Supernovae Explosions

Astrophysics and Space Science Proceedings, 2010

A better knowledge of the mechanism behind the explosion of Type Ia supernovae (SNIa) is necessary to use these events in cosmological applications such as to study the large scale geometry of the universe or to find its equation of state. We review the present status of the subject with special emphasis in the so-called pulsating models which reproduce the gross features of the explosions without using free parameters.

Thermonuclear supernova models, and observations of Type Ia supernovae

Arxiv preprint astro-ph/0412155, 2004

In this paper, we review the present state of theoretical models of thermonuclear supernovae, and compare their predicitions with the constraints derived from observations of Type Ia supernovae. The diversity of explosion mechanisms usually found in one-dimensional simulations is a direct consequence of the impossibility to resolve the flame structure under the assumption of spherical symmetry. Spherically symmetric models have been successful in explaining many of the observational features of Type Ia supernovae, but they rely on two kinds of empirical models: one that describes the behaviour of the flame on the scales unresolved by the code, and another that takes account of the evolution of the flame shape. In contrast, three-dimensional simulations are able to compute the flame shape in a self-consistent way, but they still need a model for the propagation of the flame in the scales unresolved by the code. Furthermore, in three dimensions the number of degrees of freedom of the initial configuration of the white dwarf at runaway is much larger than in one dimension. Recent simulations have shown that the sensitivity of the explosion output to the initial conditions can be extremely large. New paradigms of thermonuclear supernovae have emerged from this situacion, as the Pulsating Reverse Detonation. The resolution of all these issues must rely on the predictions of observational properties of the models, and their comparison with current Type Ia supernova data, including X-ray spectra of Type Ia supernova remnants.

Explosion Models for Thermonuclear Supernovae Resulting from Different Ignition Conditions

Springer Proceedings in Physics, 2005

We have explored in three dimensions the fate of a white dwarf of mass of 1.38M⊙ as a function of different initial locations of carbon ignition, with the aid of a SPH code. The calculated models cover a variety of possibilities ranging from the simultaneous ignition of the central volume of the star to the off-center ignition in multiple scattered spots. In the former case, the possibility of a transition to a detonation when the mean density of the nuclear flame decreases to ρ ≃ 2 10 7 g.cm −3 and its consequences are discussed. In the last case, the dependence of the results as a function of the number of initial igniting spots and the chance of some of these models to evolve to the pulsating delayed detonation scenario are also outlined.

Type Ia Supernova models arising from different distributions of igniting points

Astronomy & Astrophysics, 2005

In this paper we address the theory of Type Ia supernovae from the moment of carbon runaway up to several hours after the explosion. We have concentrated on the boiling-pot model: a deflagration characterized by the (nearly-) simultaneous ignition of a number of bubbles that pervade the core of the white dwarf. Thermal fluctuations larger than >1% of the background temperature (7x10^8 K) on lengthscales of < 1m could be the seeds of the bubbles. Variations of the homogeneity of the temperature perturbations can lead to two alternative configurations at carbon runaway: if the thermal gradient is small, all the bubbles grow to a common characteristic size related to the value of the thermal gradient, but if the thermal gradient is large enough, the size spectrum of the bubbles extends over several orders of magnitude. The explosion phase has been studied with the aid of a smoothed particle hydrodynamics code suited to simulate thermonuclear supernovae. In spite of important procedural differences and different physical assumptions, our results converge with the most recent calculations of 3D deflagrations in white dwarfs carried out in supernova studies by different groups. For large initial numbers of bubbles (>3-4 per octant), the explosion produces about 0.45 solar masses of 56Ni, and the kinetic energy of the ejecta is 0.45x10^{51} ergs. However, all three-dimensional deflagration models share three main drawbacks: 1) the scarce synthesis of intermediate-mass elements, 2) the loss of chemical stratification of the ejecta due to mixing by Rayleigh-Taylor instabilities during the first second of the explosion, and 3) the presence of big clumps of 56Ni at the photosphere at the time of maximum brightness.

Multi-spot ignition in type Ia supernova models

Astronomy & Astrophysics, 2006

We present a systematic survey of the capabilities of type Ia supernova explosion models starting from a number of flame seeds distributed around the center of the white dwarf star. To this end we greatly improved the resolution of the numerical simulations in the initial stages. This novel numerical approach facilitates a detailed study of multi-spot ignition scenarios with up to hundreds of ignition sparks. Two-dimensional simulations are shown to be inappropriate to study the effects of initial flame configurations. Based on a set of three-dimensional models, we conclude that multi-spot ignition scenarios may improve type Ia supernova models towards better agreement with observations. The achievable effect reaches a maximum at a limited number of flame ignition kernels as shown by the numerical models and corroborated by a simple dimensional analysis.

EVALUATING SYSTEMATIC DEPENDENCIES OF TYPE Ia SUPERNOVAE: THE INFLUENCE OF CENTRAL DENSITY

The Astrophysical Journal, 2012

We present a study exploring a systematic effect on the brightness of Type Ia supernovae using numerical models that assume the single-degenerate paradigm. Our investigation varied the central density of the progenitor white dwarf at flame ignition, and considered its impact on the explosion yield, particularly the production and distribution of radioactive 56 Ni, which powers the light curve. We performed a suite of two-dimensional simulations with randomized initial conditions, allowing us to characterize the statistical trends that we present. The simulations indicate that the production of Fe-group material is statistically independent of progenitor central density, but the mass of stable Fe-group isotopes is tightly correlated with central density, with a decrease in the production of 56 Ni at higher central densities. These results imply that progenitors with higher central densities produce dimmer events. We provide details of the post-explosion distribution of 56 Ni in the models, including the lack of a consistent centrally located deficit of 56 Ni, which may be compared to observed remnants. By performing a self-consistent extrapolation of our model yields and considering the main-sequence lifetime of the progenitor star and the elapsed time between the formation of the white dwarf and the onset of accretion, we develop a brightness-age relation that improves our prediction of the expected trend for single degenerates and we compare this relation with observations.

Type Ia Supernovae: Simulations and Nucleosynthesis

Nuclear Physics A, 2005

We present our first nucleosynthesis results from a numerical simulation of the thermonuclear disruption of a static cold Chandrasekhar-mass 12 C/ 16 O white dwarf. The two-dimensional simulation was performed with an adaptive-mesh Eulerian hydrodynamics code, F, that uses as a flame capturing scheme the evolution of a passive scaler. To compute the isotopic yields and their velocity distribution, 10,000 massless tracer particles are embedded in the star. The particles are advected along streamlines and provide a Lagrangian description of the explosion. We briefly describe our verification tests and preliminary results from post-processing the particle trajectories in (ρ, T) with a modest (214 isotopes) reaction network.

Detonating Failed Deflagration Model of Thermonuclear Supernovae. II. Comparison to Observations

The Astrophysical Journal, 2007

We develop and demonstrate the methodology of testing multi-dimensional supernova models against observations by studying the properties of one example of the detonation from failed deflagration (DFD) explosion model of thermonuclear supernovae. Using time-dependent multi-dimensional radiative transfer calculations, we generate the synthetic broadband optical light curves, near-infrared light curves, color evolution curves, full spectral time-series, and spectropolarization of the model, as seen from various viewing angles. All model observables are critically evaluated against examples of well-observed, standard Type Ia supernovae (SNe Ia). We explore the consequences of the intrinsic model asphericity by studying the dependence of the model emission on viewing angle, and by quantifying the resulting dispersion in (and internal correlations between) various model observables. These statistical properties of the model are also evaluated against those of the available observational sample of SNe Ia. On the whole, the DFD model shows good agreement with a broad range of SN Ia observations. Certain deficiencies are also apparent, and point to further developments within the basic theoretical framework. We also identify several intriguing orientation effects in the model which suggest ways in which the asphericity of SNe Ia may contribute to their photometric and spectroscopic diversity and, conversely, how the relative homogeneity of SNe Ia constrains the degree of asymmetry allowable in the models. The comprehensive methodology adopted in this work proves an essential component of developing and validating theoretical supernova models, and helps motivate and clearly define future directions in both the modeling and the observation of SNe Ia.