The initial reaction triggering a thermonuclear supernovaexplosion is thought to be a (12)C+(12)C reaction in the pycnonuclear regime. Such a high density is required, that it can be reached only in a white dwarf that is very compact and massive, close to the Chandrasekhar mass. I report here on work we published a short time before this conference (Chiosi et al. 2015), in which we explored the possibility that other nuclear reactions may occur in the pycnonuclear regime, namely those involving traces of hydrogen and helium, that do not produce sufficient energy to allow the white dwarf to explode, but manage to heat it and change its structure, eventually leading to a type Ia supernova explosion in a sub-Chandrasekhar mass white dwarf. This channel may even lead to the supernova explosion of isolated stars.