Thermonuclear explosion of a massive hybrid HeCO white dwarf triggered by a He detonation on a companion

Normal type la supernovae (SNe) are thought to arise from the thermonuclear explosion of massive (>0.8 M-circle dot) carbon-oxygen white dwarfs (WDs), although the exact mechanism is debated. In some models, helium accretion on to a carbon-oxygen (CO) WD from a companion was suggested to dynamically trigger a detonation of the accreted helium shell. The helium detonation then produces a shock that after converging on itself close to the core of the CO WD, triggers a secondary carbon detonation, and gives rise to an energetic explosion. However, most studies of such scenarios have been done in one or two dimensions, and/or did not consider self-consistent models for the accretion and the He donor. Here, we make use of detailed 3D simulation to study the interaction of a He-rich hybrid 0.69 M-circle dot HeCO WD with a more massive 0.8 M-circle dot CO WD. We find that accretion from the hybrid WD on to the CO WD gives rise to a helium detonation. However, the helium detonation does not trigger a carbon detonation in the CO WD. Instead, the helium detonation burns through the accretion stream to also burn the helium shell of the donor hybrid HeCO WD. The detonation of its massive helium shell then compresses its CO core, and triggers its detonation and full destruction. The explosion gives rise to a faint, likely highly reddened transient, potentially observable by the Vera Rubin survey, and the high-velocity (similar to 1000 kms(-1)) ejection of the heated surviving CO WD companion. Pending on uncertainties in stellar evolution, we estimate the rate of such transient to be up to similar to 10 per cent of the rate of type Ia SNe.

Automated summary

Normal type Ia supernovae are believed to originate from the thermonuclear explosion of massive carbon-oxygen white dwarfs, although the exact mechanism is debated. Some theories suggest that helium accretion from a companion could trigger detonations in the accreted shell. However, a study using 3D simulations found that while helium detonation occurred, it did not trigger a carbon detonation in the white dwarf.