White dwarf binaries, mergers, and explosions

Stars in binaries often have much more exciting lives, deaths, and afterlives than single ones. I will review the especially varied possibilities involving white dwarfs, which include revival and total annihilation. The latter leads to so-called type Ia supernova explosions, for which empirical calibrations of their luminosities have allowed the measurement of the acceleration of the expansion of the Universe. The standard theoretical picture, in which unstable fusion is ignited in white dwarfs that approach or are made to exceed the largest possible (Chandrasekhar) mass, has a number of problems. I will discuss these problems and will show that they would be resolved if instead, as I will propose, the ignition occurs more generally when two carbon-oxygen white dwarfs merge.