Type Ia Supernova Explosion: Gravitationally Confined Detonation (original) (raw)
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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.
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 ...
We argue that type Ia supernovae (SNe Ia) are the result of head-on collisions of White Dwarfs (WDs) in triple systems. The thermonuclear explosions resulting from the zero-impact-parameter collisions of WDs are calculated from first principles by using 2D hydrodynamical simulations. Collisions of typical WDs with masses 0.5-0.9 M_Sun result in explosions that synthesize Ni56 masses in the range of 0.15-0.8 M_Sun, spanning the wide distribution of yields observed for the majority of SNe Ia. The robustness of the shock ignition process is verified with a detailed study using a one-dimensional toy model and analytic tools. The late-time (~50 days after peak) bolometric light curve is equal to the instantaneous energy deposition and is calculated exactly, by solving the transport of gamma-rays emitted by the decay of Ni56 using a Monte-Carlo code. All collisions are found to have the same late-time light curves, when normalized to the amount of synthesized Ni56. This universal light cu...
TYPE Ia SUPERNOVAE FROM MERGING WHITE DWARFS. II. POST-MERGER DETONATIONS
The Astrophysical Journal, 2014
Merging carbon-oxygen (CO) white dwarfs are a promising progenitor system for Type Ia supernovae (SN Ia), but the underlying physics and timing of the detonation are still debated. If an explosion occurs after the secondary star is fully disrupted, the exploding primary will expand into a dense CO medium that may still have a disk-like structure. This interaction will decelerate and distort the ejecta. Here we carry out multi-dimensional simulations of "tamped" SN Ia models, using both particle and grid-based codes to study the merger and explosion dynamics, and a radiative transfer code to calculate synthetic spectra and light curves. We find that post-merger explosions exhibit an hourglass-shaped asymmetry, leading to strong variations in the light curves with viewing angle. The two most important factors affecting the outcome are the scale-height of the disk, which depends sensitively on the binary mass ratio, and the total 56 Ni yield, which is governed by the central density of the remnant core. The synthetic broadband light curves rise and decline very slowly, and the spectra generally look peculiar, with weak features from intermediate mass elements but relatively strong carbon absorption. We also consider the effects of the viscous evolution of the remnant, and show that a longer time delay between merger and explosion probably leads to larger 56 Ni yields and more symmetrical remnants. We discuss the relevance of this class of aspherical "tamped" SN Ia for explaining the class of "super-Chandrasekhar" SN Ia.
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.
Pulsating reverse detonation models of Type Ia supernovae. II: Explosion
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) foes, and 56Ni masses, M(56Ni) ~ 0.6-0.8 M_sun, 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.
The response of a helium white dwarf to an exploding Type Ia supernova
Monthly Notices of the Royal Astronomical Society, 2015
We conduct numerical simulations of the interacting ejecta from an exploding CO white dwarf (WD) with the He WD donor in the double-detonation scenario for Type Ia supernovae (SNe Ia), and find that the descendant supernova remnant (SNR) is highly asymmetrical, in contradiction with observations. When the donor He WD has low mass, M WD = 0.2M ⊙ , it is at a distance of ∼ 0.08R ⊙ from the explosion, and helium is not ignited. The low mass He WD casts an 'ejecta shadow' behind it, that has imprint in the SN remnant (SNR) hundreds of years later. The outer parts of the shadowed side are fainter and its boundary with the ambient gas is somewhat flat. These features are not found in known SNRs. More massive He WD donors, M WD ≃ 0.4M ⊙ , must be closer to the CO WD to transfer mass. At a distance a 0.045R ⊙ helium is ignited and the He WD explodes. This explosion leads to a highly asymmetrical SNR and to ejection of ∼ 0.15M ⊙ of helium, both of which contradict observations of SNe Ia.
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.
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.