Type Ia supernovae (SNe Ia) signal the death of a star in a thermonuclear runaway. While most, if not all, are believed to result from the disruption of white dwarf stars, the details of how, where and when these explosions occur remain elusive.
With the advent of wide-field, high-cadence surveys, SNe Ia are now routinely watched on prime seats, from hours to days after the onset of the explosion. These data suggest that there are likely multiple evolutionary pathways leading to SN Ia explosions. Explaining this diversity is key, not only for Cosmology applications, but also for understanding chemical enrichment, galaxy feedback and stellar evolution.
In my talk, I will elaborate on some recent breakthroughs in our understanding of intermediate mass helium stars — objects that are generally thought to form low-mass neutron stars. I will describe how some of these objects evolve into highly degenerate, near-Chandrasekhar mass cores with helium-deficient envelopes, that subsequently ignite carbon and oxygen explosively at relatively low densities.
This happens either due to compression from shell burning (when the core has a hybrid CO/NeO composition), or following ignition of residual carbon triggered by exothermic electron captures on magnesium-24 (for a NeOMg-dominated composition). The resulting thermonuclear runaways are likely to prevent core collapse, leading to the complete disruption of the star in a SN Ia explosion.
The frequency of progenitor systems suffices to account for the majority of explosions in star-forming galaxies and may explain the abundances of some heavy elements in the Solar System.