Non-equilibrium Phenomena in Thermonuclear Supernovae: from life to death of white dwarf stars

Abstract

In this thesis we investigate some non-equilibrium phenomena in the dynamics of evolutional stages of white dwarfs, such as cooling and Type Ia supernova explosions. The first part of the thesis is dedicated to introduction of the general concept of non- equilibrium thermodynamics, and its application in describing transient phenomena in systems near-equilibrium which are very common in Nature. In particular, we present the context of astrophysical systems focusing on the physical ingredients present inside white dwarf stars, which are the progenitors of type Ia supernovae. In the second part of the thesis, we deal with white dwarf stars, more precisely their thermal evolution as a stationary state of thermodynamics. Since the nuclear fusion processes have been ceased in these stars, their thermal energy stored during the period as proto-white dwarf is the only source of their luminosity as an almost steady energy from the core region to the surface. In this thesis, we introduce a very simple model for such a process of white dwarfs cooling, and derive a simple analytic expression which constrains their radii, masses and effective temperatures, as they cool. The third and final part of the thesis is devoted to the study of retardation effects on hydrodynamic calculations, more precisely on the delayed thermalization of the smallest fluid element considered numerically. Below the length scale defined by this element of fluid, transient phenomena are ignored by many numerical calculations. This thesis is dedicated mainly to the improvement of some numerical methods used for the simulation of thermonuclear supernovas, taking into account a simplified model of the retardation effects coming from transient processes, well described by non-equilibrium thermodynamics. We have verified that the delayed thermalization effects in the material can be determined by its signatures on the supernova observables, such as nucleosynthesis and energy released during the explosion.

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