Type Ia Supernova models arising from different distributions of igniting points^*

¹ Departament de Física i Enginyeria Nuclear, UPC, Sor Eulalia d'Anzizu s/n, B5, 08034 Barcelona, Spain e-mail: [domingo.garcia;eduardo.bravo]@upc.es
² Institut d'Estudis Espacials de Catalunya, Spain

Received: 9 July 2004
Accepted: 2 September 2004

Abstract

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 (~ K) on lengthscales of 1 m 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 three-dimensional 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 ~ of ⁵⁶Ni, and the kinetic energy of the ejecta is ~ 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. On the other hand, if the initial number of igniting bubbles is small enough, the explosion fails, the white dwarf oscillates, and a new opportunity comes for a detonation to ignite and process the infalling matter after the first pulsation.