The Diversity of Type Ia Supernovae from Broken Symmetries

TL;DR

This paper uses multi-dimensional models to show that asymmetries in Type Ia supernova explosions significantly influence their brightness and light curve width, affecting their use as standard candles in cosmology.

Contribution

It demonstrates that breaking spherical symmetry is crucial for understanding supernova brightness relations and observed scatter, with implications for cosmic distance measurements.

Findings

Asymmetries affect the width-luminosity relation.

Breaking symmetry explains supernova polarization.

Progenitor composition weakly influences the relation.

Abstract

Type Ia supernovae result when carbon-oxygen white dwarfs in binary systems accrete mass from companion stars, reach a critical mass, and explode. The near uniformity of their light curves makes these supernovae good standard candles for measuring cosmic expansion, but a correction must be applied to account for the fact that the brighter supernovae have broader light curves. One-dimensional modelling, with a certain choice of parameters, can reproduce this general trend in the width-luminosity relation, but the processes of ignition and detonation have recently been shown to be intrinsically asymmetric. Here we report on multi-dimensional modelling of the explosion physics and radiative transfer that reveals that the breaking of spherical symmetry is a critical factor in determining both the width luminosity relation and the observed scatter about it. The deviation from sphericity can also explain the finite polarization detected in the light from some supernovae. The slope and normalization of the width-luminosity relation has a weak dependence on certain properties of the white dwarf progenitor, in particular the trace abundances of elements other than carbon and oxygen. Failing to correct for this effect could lead to systematic overestimates of up to 2% in the distance to remote supernovae.