  In the framework of the Chandrasekhar-mass deflagration model for Type Ia
supernovae (SNe Ia), a persisting free parameter is the initial morphology of
the flame front, which is linked to the ignition process in the progenitor
white dwarf. Previous analytical models indicate that the thermal runaway is
driven by temperature perturbations (''bubbles'') that develop in the white
dwarf's convective core. In order to probe the conditions at ignition
(diameters, temperatures and evolutionary timescales), we have performed
hydrodynamical 2D simulations of buoyant bubbles in white dwarf interiors. Our
results show that fragmentation occurring during the bubble rise affects the
outcome of the bubble evolution. Possible implications for the ignition process
of SNe Ia are discussed.
