In white dwarfs, the core of the star is cold, under which conditions, so, if treated classically, the nuclei that arrange themselves into a crystal lattice are in their ground state. The zero-point oscillations of nuclei in the crystal lattice with energy at the energy  at Gamow's peak equal to  can overcome the Coulomb barrier, actuating pycnonuclear reactions. A semi-analytical model indicates that in white dwarfs, a thermonuclear runaway can occur at much earlier ages than that of the universe, as the pycnonuclear reactions in the cores of white dwarfs exceed the luminosity of the white dwarfs, allowing C-burning to occur, which catalyzes the formation of type Ia supernovas in accreting white dwarfs, whose mass is equal to the Chandrasekhar mass.
Some studies indicate that the contribution of pycnonuclear reactions towards instability of white dwarfs is only significant in carbon white dwarfs, while in oxygen white dwarfs, such instability is caused mostly due to electron capture. Although other authors disagree that the pycnonuclear reactions can act as major long-term heating sources for massive (1.25 ) white dwarfs, as their density would not suffice for a high rate of pycnonuclear reactions.
While most studies indicate that at the end of their lifecycle, white dwarfs slowly decay into black dwarfs, where pycnonuclear reactions slowly turn their cores into , according to some versions, a collapse of black dwarfs is possible: M.E. Caplan (2020) theorizes that in the most massive black dwarfs (1.25 ), due to their declining electron fraction resulting from  production, they will exceed the Chandrasekhar limit in the very far future, speculating that their lifetime and delay time can stretch to up to  years.