Type Ia Supernova models arising from different distributions of igniting points (original) (raw)
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Single and multiple detonations in white dwarfs
Astronomy and Astrophysics
A currently favored model for Type Ia supernovae consists of a carbon-oxygen (CO) white dwarf ( ~ 0.6-1.0 M_sun), surrounded by a thick layer of helium ( ~ 0.2-0.3 M_sun), which explodes as a consequence of successive detonations in the helium layer and the CO core. Previous studies, carried out in one and two dimensions, have shown that this model is capable of providing light curves and late-time spectra in agreement with observations, though the peak light spectrum may be problematic. These same studies also highlighted a key uncertainty in the model. When properly considered in three dimensions, will the helium detonation actually succeed in igniting a corresponding detonation in the carbon core? In this paper we follow the hydrodynamic evolution of a representative case calculated in three dimensions using the smoothed particle (SPH) approach to multi-dimensional hydrodynamical modeling. Several fine zoned simulations are also carried out in one dimension to elucidate shock hyd...
Beyond the Bubble Catastrophe of Type Ia Supernovae: Pulsating Reverse Detonation Models
The Astrophysical Journal, 2006
We describe a mechanism by which a failed deflagration of a Chandrasekharmass carbon-oxygen white dwarf can turn into a successful thermonuclear supernova explosion, without invoking an ad hoc high-density deflagration-detonation transition. Following a pulsating phase, an accretion shock develops above a core of ∼ 1 M ⊙ composed of carbon and oxygen, inducing a converging detonation. A three-dimensional simulation of the explosion produced a kinetic energy of 1.05 × 10 51 ergs and 0.70 M ⊙ of 56 Ni, ejecting scarcely 0.01 M ⊙ of C-O moving at low velocities. The mechanism works under quite general conditions and is flexible enough to account for the diversity of normal Type Ia supernovae. In given conditions the detonation might not occur, which would reflect in peculiar signatures in the gamma and UV-wavelengths.
2006
We present a detonating failed deflagration model of Type Ia supernovae. In this model, the thermonuclear explosion of a massive white dwarf follows an off-center deflagration. We conduct a survey of asymmetric ignition configurations initiated at various distances from the stellar center. In all cases studied, we find that only a small amount of stellar fuel is consumed during deflagration phase, no explosion is obtained, and the released energy is mostly wasted on expanding the progenitor. Products of the failed deflagration quickly reach the stellar surface, polluting and strongly disturbing it. These disturbances eventually evolve into small and isolated shock-dominated regions which are rich in fuel. We consider these regions as seeds capable of forming self-sustained detonations that, ultimately, result in the thermonuclear supernova explosion. Preliminary nucleosynthesis results indicate the model supernova ejecta are typically composed of about 0.1−0.25 M ⊙ of silicon group ...
Detonating Failed Deflagration Model of Thermonuclear Supernovae I. Explosion Dynamics
We present a detonating failed deflagration model of Type Ia supernovae. In this model, the thermonuclear explosion of a massive white dwarf follows an off-center deflagration. We conduct a survey of asymmetric ignition configurations initiated at various distances from the stellar center. In all cases studied, we find that only a small amount of stellar fuel is consumed during deflagration phase, no explosion is obtained, and the released energy is mostly wasted on expanding the progenitor. Products of the failed deflagration quickly reach the stellar surface, polluting and strongly disturbing it. These disturbances eventually evolve into small and isolated shock-dominated regions that are rich in fuel. We consider these regions as seeds capable of forming self-sustained detonations that, ultimately, result in the thermonuclear super-nova explosion. Preliminary nucleosynthesis results indicate that the model supernova ejecta are typically composed of about 0:1Y0:25 M of silicon group elements and 0:9Y1:2 M of iron group elements and are essentially carbon-free. The ejecta have a composite morphology, are chemically stratified, and display a modest amount of intrinsic asymmetry. The innermost layers are slightly egg shaped with the axis ratio %1.2Y1.3 and dominated by the products of silicon burning. This central region is surrounded by a shell of silicon group elements. The outermost layers of ejecta are highly inhomogeneous and contain products of incomplete oxygen burning with only small admixture of unburned stellar material. The explosion energies are %(1:3Y1:5) ; 10 51 ergs.
Detonations in white dwarf dynamical interactions
Monthly Notices of the Royal Astronomical Society, 2013
In old, dense stellar systems collisions of white dwarfs are a rather frequent phenomenon. Here we present the results of a comprehensive set of Smoothed Particle Hydrodynamics simulations of close encounters of white dwarfs aimed to explore the outcome of the interaction and the nature of the final remnants for different initial conditions. Depending on the initial conditions and the white dwarf masses, three different outcomes are possible. Specifically, the outcome of the interaction can be either a direct or a lateral collision or the interaction can result in the formation of an eccentric binary system. In those cases in which a collision occurs, the infalling material is compressed and heated such that the physical conditions for a detonation may be reached during the most violent phases of the merger. While we find that detonations occur in a significant number of our simulations, in some of them the temperature increase in the shocked region rapidly lifts degeneracy, leading to the quenching of the burning. We thus characterize under which circumstances a detonation is likely to occur as a result of the impact of the disrupted star on the surface of the more massive white dwarf. Finally, we also study which interactions result in bound systems, and in which ones the more massive white dwarf is also disrupted as a consequence of the dynamical interaction. The sizable number of simulations performed in this work allows to find how the outcome of the interaction depends on the distance at closest approach, and on the masses of the colliding white dwarfs, and which is the chemical pattern of the nuclearly processed material. Finally, we also discuss the influence of the masses and core chemical compositions of the interacting white dwarfs and the different kinds of impact in the properties of the remnants.
The Astrophysical Journal, 2007
The explosion of a carbon-oxygen white dwarf as a Type Ia supernova is known to be sensitive to the manner in which the burning is ignited. Studies of the pre-supernova evolution suggest asymmetric, off-center ignition, and here we explore its consequences in two-and three-dimensional simulations. Compared with centrally ignited models, one-sided ignitions initially burn less and release less energy. For the distributions of ignition points studied, ignition within two hemispheres typically leads to the unbinding of the white dwarf, while ignition within a small fraction of one hemisphere does not. We also examine the spreading of the blast over the surface of the white dwarf that occurs as the first plumes of burning erupt from the star. In particular, our studies test whether the collision of strong compressional waves can trigger a detonation on the far side of the star as has been suggested by Plewa et al. (2004). The maximum temperature reached in these collisions is sensitive to how much burning and expansion has already gone on, and to the dimensionality of the calculation. Though detonations are sometimes observed in 2D models, none ever happens in the corresponding 3D calculations. Collisions between the expansion fronts of multiple bubbles also seem, in the usual case, unable to ignite a detonation. "Gravitationally confined detonation" is therefore not a robust mechanism for the explosion. Detonation may still be possible in these models however, either following a pulsation or by spontaneous detonation if the turbulent energy is high enough.
Type Ia supernovae: an asymmetric deflagration model
Arxiv preprint astro-ph/ …, 2004
We present the first high-resolution three-dimensional simulations of the deflagration phase of Type Ia supernovae that treat the entire massive white dwarf. We report the results of simulations in which ignition of the nuclear burning occurs slightly off-center. The subsequent evolution of the nuclear burning is surprisingly asymmetric with a growing bubble of hot ash rapidly rising to the stellar surface. Upon reaching the surface, the mass of burned material is ≈ 0.075M ⊙ and the kinetic energy is 4.3 × 10 49 ergs. The velocity of the top of the rising bubble approaches 8000 km s −1 . The amount of the asymmetry found in the model offers a natural explanation for the observed diversity in Type Ia supernovae. Our study strongly disfavors the classic central-ignition pure deflagration scenario by showing that the result is highly sensitive to details of the initial conditions.
Thermonuclear Supernovae: Is Deflagration Triggered by Floating Bubbles?
ESO ASTROPHYSICS SYMPOSIA, 2003
In recent years, it has become clear from multidimensional simulations that the outcome of deflagrations depends strongly on the initial configuration of the flame. We have studied under which conditions this configuration could consist of a number of scattered, isolated, hot bubbles. Afterwards, we have calculated the evolution of deflagrations starting from different numbers of bubbles. We have found that starting from 30 bubbles a mild explosion is produced (M ( 56 Ni) = 0.56M⊙), while starting from 10 bubbles the star becomes only marginally unbound (K = 0.05 foes).
Astrophysics and Space Science, 1987
We present models for Type I supernova light curves based on the explosion of partially solid white dwarfs in close binary systems. Studies of such explosions show that they leave bound remnants of different size. Our results reproduce quite well the maximun luminosities, the expansion velocities and the shape of the light curve. As the two basic parameters that govern the light curve, the ejected mass and the mass of Ni produced, are variable our models reproduce the slow and fast subclasses of "classical" Type I supernovae.
The Thermonuclear Explosion of Chandrasekhar Mass White Dwarfs
The Astrophysical Journal, 1997
The flame born in the deep interior of a white dwarf that becomes a Type Ia supernova is subject to several instabilities, the combination of which determines the observational characteristics of the explosion. We briefly review these instabilities and discuss the length scales for which each dominates. Their cumulative effect is to accelerate the speed of the flame beyond its laminar value, but that acceleration has uncertain time and angle dependence which has allowed numerous solutions to be proposed (e.g., deflagration, delayed detonation, pulsational deflagration, and pulsational detonation). We discuss the conditions necessary for each of these events and the attendant uncertainties. A grid of critical masses for detonation in the range 10 7-2 × 10 9 g cm −3 is calculated and its sensitivity to composition explored. The conditions for prompt detonation are discussed. Such explosions are physically improbable and appear unlikely on observational grounds. Simple deflagrations require some means of boosting the flame speed beyond what currently exists in the literature. "Active turbulent combustion" and multi-point ignition are presented as two plausible ways of doing this. A deflagration that moves at the "Sharp-Wheeler" speed, 0.1g eff t, is calculated in one dimension and shows that a healthy explosion is possible in a simple deflagration if fuel can be efficiently burned behind a front that moves with the speed of the fastest floating bubbles generated by the non-linear Rayleigh-Taylor instability. The relevance of the transition to the "distributed regime" of turbulent nuclear burning is discussed for delayed and pulsational detonations. This happens when the flame speed has slowed to the point that turbulence can actually penetrate the flame thickness and may be advantageous for producing the high fuel temperatures and gentle temperature gradients necessary for detonation. No model emerges without difficulties, but detonation in the distributed regime is plausible, will produce intermediate mass elements, and warrants further study. The other two leading models, simple deflagration and pulsational detonation, are mutually exclusive.