Sub-luminous type Ia supernovae from the mergers of equal-mass white dwarfs with mass 0.9M

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Type Ia supernovae are thought to result from thermonuclear explosions of carbon–oxygen white dwarf stars1. Existing models2 generally explain the observed properties, with the exception of the sub-luminous 1991bg-like supernovae3. It has long been suspected that the merger of two white dwarfs could give rise to a type Ia event4,5, but hitherto simulations have failed to produce an explosion6,7. Here we report a simulation of the merger of two equal-mass white dwarfs that leads to a sub-luminous explosion, although at the expense of requiring a single common-envelope phase, and component masses of 0.9M. The light curve is too broad, but the synthesized spectra, red colour and low expansion velocities are all close to what is observed for sub-luminous 1991bg-like events. Although the mass ratios can be slightly less than one and still produce a sub-luminous event, the masses have to be in the range 0.83M to 0.9M.

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Figure 1: Time evolution of the binary system.
Figure 2: Synthetic light curves of our model.
Figure 3: Synthetic spectrum of our model.


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We thank K. Belczynski for supporting the population synthesis analysis and S. Taubenberger and S. Hachinger for discussions. This work was supported by the Transregional Research Centre “The Dark Universe” of the German Research Foundation and by the Excellence Cluster “Origin and Structure of the Universe”. The work of F.K.R. is supported through the Emmy Noether Program of the German Research Foundation. We are grateful for computer time provided by the Computer Centre of the Max Planck Society in Garching, where all simulations were performed.

Author Contributions R.P. carried out the hydrodynamical simulations and the nucleosynthesis postprocessing. M.K. performed the radiative transfer simulations. F.K.R. and R.P. worked on development of the hydrocodes. S.A.S. and M.K. developed the radiative transfer code. W.H. and F.K.R. started the project. A.J.R. analysed the results of population synthesis calculations. All authors contributed to the interpretation of the simulations and to the writing of the paper.

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Correspondence to Rüdiger Pakmor.

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