The physics of type Ia supernovae

Abstract

The basic recipe for SN Ia explosions is simple. A white dwarf in a binary system, growing towards the limiting Chandrasekhar mass, contracts and ignites under degenerate (electron gas) conditions, causing a thermonuclear runaway. Burning 1.4 M ⊙ of 12C and 16O in equal proportions to 1.398776 M ⊙ of 56Ni releases the mass difference in nuclear binding energy, i.e., a thermonuclear explosion of about about 2.19×10 51 erg, which disrupts the original white dwarf completely. The subtraction of the gravitational binding energy of the white dwarf of (≈(5–6)×10 50 erg), plus the observed fact that not all material is burned to Fe/Ni (rather to intermediate elements like Mg, Si, S, Ca), leads to the observed explosion energies (≈1.3×10 51 erg). The decay chain 56Ni → 56Co → 56Fe can explain the lightcurve. The remaining questions are: how can cool and stable white dwarfs be turned into exploding objects via binary mass exchange; what variety of original white dwarf sizes, metallicities and accretion scenarios is expected; how does the ignition occur and does the burning front propagate; how does this relate to burning conditions, energy generation, nucleosynthesis results, 56Ni masses and the small observed variety in explosive events; how can observed spectra (and their Doppler broadening) act as diagnostics for explosion models and nucleosynthesis predictions? We will address these issues within existing 1D spherically symmetric models with parameterized burning front prescriptions and attempt to discuss the relation to multi-D models.