Chandrasekhar-mass or sub-Chandrasekhar-mass white dwarfs in normal Type Ia supernovae
In plain words
The exploding white dwarf may be close to the maximum mass a white dwarf can have (about 1.4 Suns), or lighter, with a helium layer on its surface detonating first and setting off the core. Each picture predicts different elements in the debris.
Precise statement
For normal SNe Ia, decide whether the exploding white dwarf is near $M_{\mathrm{Ch}} = 1.38\,M_{\mathrm{sun}}$ with a deflagration-to-detonation transition, or at $0.9\ \text{to}\ 1.1\,M_{\mathrm{sun}}$ exploding by a helium-shell detonation that triggers a carbon-oxygen core detonation (double detonation), and give the fraction of each. Discriminating observables include $\mathrm{Mn}/\mathrm{Fe}$ and stable $\mathrm{Ni}/\mathrm{Fe}$ in ejecta and nebular spectra, the stratification of Ca and other intermediate-mass elements in young remnants, and early-time spectra.
What would settle it
Nebular-phase stable Ni and Mn yields and remnant element stratification for a statistical sample, compared with 3D explosion models of both classes.
Status in the literature
Unverified note
In 2025 a double calcium shell in the young Large Magellanic Cloud remnant SNR 0509-67.5 was reported as the predicted signature of a double detonation (Das et al., Nature Astronomy, 2025); whether this is the common route remains open.