A unified mechanism for unconfined deflagration-to-detonation transition in terrestrial chemical systems and type Ia supernovae (original) (raw)
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Monthly Notices of the Royal Astronomical Society: Letters, 2020
Our aim in this work is to identify and explain the necessary conditions required for an energetic explosion of a Chandrasekhar-mass white dwarf. We construct and analyse weakly compressible turbulence models with nuclear burning effects for carbon/oxygen plasma at a density expected for the deflagration-to-detonation transition (DDT) to occur. We observe the formation of carbon deflagrations and transient carbon detonations at early times. As turbulence becomes increasingly inhomogeneous, sustained carbon detonations are initiated by the Zel’dovich reactivity gradient mechanism. The fuel is suitably preconditioned by the action of compressive turbulent modes with wavelength comparable to the size of resolved turbulent eddies; no acoustic wave is involved in this process. Oxygen detonations are initiated, aided either by reactivity gradients or by collisions of carbon detonations. The observed evolutionary time-scales are found to be sufficiently short for the above process to occur...
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 ...
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.
The Astrophysical Journal, 2007
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.
Constraints on the Delayed Transition to Detonation in Type Ia Supernovae
The Astrophysical Journal, 2000
We investigate the possibility of a delayed detonation scenario within a type Ia supernova in a case where the transition to detonation is assumed to be triggered by turbulence only. Our results are based on the Zeldovich mechanism and suggest that typical turbulent velocities present during the explosion are not strong enough to allow this transition. Although we are able to show that carbon-rich matter (e.g., X(12 C) = 0.75) significantly enhances the possibility of a deflagration to detonation transition (DDT), it turns out that even in this case the necessary turbulent velocities are larger than the expected vlaue of u ′ (L) ≈ 10 7 cm s −1 on a length-scale of L ≈ 10 6 cm. Thus we conclude that a DDT may not be a common event during a thermonuclear explosion of a chandrasekhar-mass white dwarf.
CARBON DEFLAGRATION IN TYPE Ia SUPERNOVA. I. CENTRALLY IGNITED MODELS
The Astrophysical Journal, 2013
A leading model for Type Ia supernovae (SNe Ia) begins with a white dwarf near the Chandrasekhar mass that ignites a degenerate thermonuclear runaway close to its center and explodes. In a series of papers, we shall explore the consequences of ignition at several locations within such dwarfs. Here we assume central ignition, which has been explored before, however, the problem is worth revisiting, if only to validate those previous studies and to further elucidate the relevant physics for future work. A perturbed sphere of hot iron ash with a radius of ∼100 km is initialized at the middle of the star. The subsequent explosion is followed in several simulations using a thickened flame model in which the flame speed is either fixed -within the range expected from turbulent combustionor based on the local turbulent intensity. Global results, including the explosion energy and bulk nucleosynthesis (e.g. 56 Ni of 0.48-0.56 M ⊙ ) turn out to be insensitive to this speed. In all completed runs, the energy released by the nuclear burning is adequate to unbind the star, but not enough to give the energy and brightness of typical SNe Ia. As found previously, the chemical stratification observed in typical events is not reproduced. These models produce a large amount of unburned carbon and oxygen in central low velocity regions, which is inconsistent with spectroscopic observations, and the intermediate mass elements and iron group elements are strongly mixed during the explosion.
Parametric transition from deflagration to detonation in stellar medium
Physical Review E
The nature of thermonuclear explosions of white-dwarf stars is a fundamental astrophysical issue, the first principle interpretation of which is still commonly regarded as an unresolved problem. There is a general consensus that stellar explosions are a manifestation of the deflagration-to-detonation transition of an outward propagating self-accelerating thermonuclear flame subjected to instability-induced corrugations. A similar problem arises in unconfined terrestrial flames where a positive feedback mechanism leading to the pressure runaway has been identified. The present study is an application of this finding to the stellar environment. Notwithstanding a substantial modification of the equation of state the runaway effect endures. Approaching the runaway point the pretransition flame may stay perfectly subsonic, which challenges the view that to ensure the transition the flame should cross the threshold of Chapman-Jouguet deflagration.
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.
PULSATING REVERSE DETONATION MODELS OF TYPE Ia SUPERNOVAE. I. DETONATION IGNITION
The Astrophysical Journal, 2009
Observational evidences point to a common explosion mechanism of Type Ia supernovae based on a delayed detonation of a white dwarf. However, all attempts to find a convincing ignition mechanism based on a delayed detonation in a destabilized, expanding, white dwarf have been elusive so far. One of the possibilities that has been invoked is that an inefficient deflagration leads to pulsation of a Chandrasekhar-mass white dwarf, followed by formation of an accretion shock that confines a carbon-oxygen rich core, while transforming the kinetic energy of the collapsing halo into thermal energy of the core, until an inward moving detonation is formed. This chain of events has been termed Pulsating Reverse Detonation (PRD). In this work we present three dimensional numerical simulations of PRD models from the time of detonation initiation up to homologous expansion. Different models characterized by the amount of mass burned during the deflagration phase, M defl , give explosions spanning a range of kinetic energies, K ∼ (1.0 − 1.2) × 10 51 erg, and 56 Ni masses, M ( 56 Ni) ∼ 0.6 − 0.8 M ⊙ , which are compatible with what is expected for typical Type Ia supernovae. Spectra and light curves of angle-averaged spherically symmetric versions of the PRD models are discussed. Type Ia supernova spectra pose the most stringent requirements on PRD models.
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.