The diversity of type Ia supernovae from broken symmetries

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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 expansion1,2,3,4, but a correction must be applied to account for the fact that the brighter ones have broader light curves5. One-dimensional modelling, with a certain choice of parameters, can reproduce this general trend in the width–luminosity relation6,7,8; but the processes of ignition and detonation have recently been shown to be intrinsically asymmetric9,10,11,12,13, so parameterization must have its limits. Here we report multi-dimensional modelling of the explosion physics and radiative transfer, which 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 spherical symmetry can also explain the finite polarization detected in the light from some supernovae14. 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 per cent in the distance to remote supernovae.

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Figure 1: Chemical structure of the ejected debris 100 s after ignition for a subset of the explosion models with different ignition and detonation conditions.
Figure 2: Synthetic multi-colour light curves and spectra of a representative explosion model compared to observations of a normal type Ia supernova.
Figure 3: Correlation of the peak brightness of the models with their light-curve duration and colour.
Figure 4: Effect of the metal content of the progenitor star population on the WLR.


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D.K. and S.E.W. thank the Max Planck Institute for Astrophysics for hospitality during a visit when much of this research was carried out. Support for this work was provided by the DOE SciDAC Program. Support for D.K. was provided by NASA through a Hubble fellowship grant awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA. The research of F.K.R. is supported through the Emmy Noether Program of the German Research Foundation. We are grateful for computer time provided by NERSC and ORNL through an INCITE award.

Author Contributions D.K. developed and ran the radiative transfer calculations used to generate synthetic light curves and spectra of the models, and performed analysis and comparison to observations. F.K.R. set up the initial model conditions and ran the series of hydrodynamical explosion models. S.E.W. provided insight into the parameterization of ignition, detonation and electron capture, and assisted with the analysis.

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Correspondence to D. Kasen.

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Kasen, D., Röpke, F. & Woosley, S. The diversity of type Ia supernovae from broken symmetries. Nature 460, 869–872 (2009) doi:10.1038/nature08256

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