Stability of supernova Ia progenitors against radial oscillations

We analyze the possible existence of a pulsational instability excited by the ε-mechanism during the last few centuries of evolution of a Chandrasekhar-mass white dwarf prior to its explosion as a Type la supernova. Our analysis is motivated by the temperature sensitivity of the nuclear energy generation rate (∼T²³) in a white dwarf whose structural adiabatic index is near 4/3. Based on a linear stability analysis, we find that the fundamental mode and higher order radial modes are indeed unstable and that the fundamental mode has the shortest growth timescale. However, the growth timescale for such instability never becomes shorter than the evolutionary time-scale. Therefore, even though the star is pulsationally unstable, we do not expect these radial modes to have time to grow and to affect the structure and explosion properties of Type la supernovae.