From Single Degenerate Quiescent Helium Accretion to Double Detonation Type Ia Supernova

We investigate the sub-Chandrasekhar mass double detonation pathway as a viable mechanism for Type Ia supernovae, focusing on systems arising from single degenerate carbon–oxygen (CO) white dwarfs (WDs) that accrete helium. Building upon our previous one-dimensional study of recurrent helium novae (Hillman et al. 2025), we modeled the secular evolution of a 0.7 M⊙​ WD. This WD was evolved through steady helium accretion at a relatively slow rate of 10−8 M⊙​ yr−1 until it reached a critical mass of 1.1 M⊙​. This detailed evolution yielded realistic, time-evolved temperature and composition profiles within the WD and its helium layer.

These time-evolved profiles were then mapped into the multi-dimensional hydrodynamic code FLASH, which incorporates a sophisticated reaction network for nuclear burning in both the helium shell and the CO core. The simulations were initiated by introducing a localized, modest temperature perturbation near the base of the helium shell. This subtle trigger robustly instigated an outward-propagating helium-shell detonation. The resulting inward-propagating shock wave from the helium detonation converged strongly near the center of the CO core, igniting a secondary, catastrophic carbon–oxygen detonation that completely unbinds the star.

We report a total 56Ni yield of ≃0.64M⊙​, an intermediate-mass element (Si-Ca) mass of ≃0.41M⊙​, and maximum ejecta velocities approaching ∼22,000 km s−1. These key characteristic values are consistent with observations of normal, cosmologically useful Type Ia supernovae. Our results compellingly demonstrate that recurrent helium accretors, systems typically characterized by long quiescent timescales, can evolve under subtle, "quiet" conditions to trigger robust double detonations, firmly supporting their role as viable and important progenitors of sub-Chandrasekhar mass Type Ia supernovae.