Special TAPIR Seminar
Abstract: White dwarf stars are the most common remnant of stars after they die. Unlike our Sun, most stars are born orbiting with a companion star in a binary. White dwarfs in binary star systems can explode as Type Ia supernova explosions, which are frequently observed in distant Galaxies (Nobel Prize in Physics 2011).
In the past few years, the Zwicky Transient Facility (ZTF) has detected dozens of nearby double white dwarf binaries which should merge in the next thousands of years. To our surprise, all of these white dwarfs are hot and large. In this talk I will summarise our recently published work (McNeill and Hirai 2025). Inspired by the success of tidal heating theory in explaining temperatures of hot-Jupiter exoplanets, we generalised the theory of tidal heating to white dwarf stars. Tidal forces inevitably heat up, and inflate white dwarfs in short period binaries (orbiting faster than ~ once per hour), consistent with the emerging observational context from ZTF. This restricts the kinds of binary star systems which make Type Ia supernovae, disfavouring the double degenerate scenario for type Ia supernovae progenitors.
Time permitting, I will also introduce some recent work related to exploding massive stars. While these rare stars only make up ~1% of the population, their terminal explosions at the collapse of their iron cores power the most energetic explosions in the Universe. For example, the core collapse of rapidly rotating massive stars are thought to produce the long gamma ray bursts which accompany Type Ic supernova explosions. I will present a new 3D simulation of a rapidly rotating Wolf-Rayet star during the final oxygen (O) shell burning phase. Rather than well-defined rigidly rotating convective regions, specific angular momentum prefers to be mixed across the whole star. This dynamical state should be realised for any massive star which undergoes a convective "shell merger", which are thought to occur between O/Ne/C shells in at least 40% of core-collapse progenitors. I will show that pre-collapse shell mergers can provide initial conditions required for the most energetic magnetar-driven explosions ~10^52 erg, currently unattainable in 3D core-collapse explosion simulations.