Type Ia Supernovae Can Arise from the Detonations of Both Stars in a Double Degenerate Binary

The precise origin of Type Ia supernovae (SNe Ia) is unknown despite theirvalue to numerous areas in astronomy. While it is a long-standing consensusthat they arise from an explosion of a carbon/oxygen white dwarf, the exactprogenitor configurations and explosion mechanisms that lead to SNe Ia arestill debated. One popular theory is the double detonation in which a heliumlayer, accreted from a binary companion, detonates on the surface of theprimary star, leading to a converging shock-induced detonation of theunderlying core. It has recently been seen in simulations that a helium-richdegenerate companion may undergo its own explosion triggered by the impact fromthe ejecta of the primary star. We show 2D simulations that model a white dwarfundergoing a double detonation which triggers the explosion of the degeneratecompanion, leading to either a triple or quadruple detonation. We also presentthe first multi-dimensional radiative transfer results from the triple andquadruple detonation scenario. We find that within a range of massconfigurations of the degenerate binary, the synthetic light curves and spectraof these events match observations as well as theoretical models of isolateddouble detonations do. Notably, double and quadruple detonations that arespectrally similar and reach the same peak brightnesses have drasticallydifferent ejection masses and produce different amounts of Si- and Fe-groupelements. Further understanding of this scenario is needed in order todetermine if at least some observed SNe Ia actually originate from two starsexploding.