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Death by Dynamics: Planetoid-Induced Explosions on White Dwarfs

At intervals as short as ten thousand years, each white dwarf (WD) passes within a solar radius of a planetoid, i.e., a comet, asteroid, or planet. Gravitational tidal forces tear the planetoid apart; its metal-rich debris falls onto the WD, enriching the atmosphere. A third of WDs exhibit atmospheric "pollution". For roughly every hundred planetoid disruptions, a planetoid collides with a WD. We simulate a small number of collisions, in which "death-by-dynamics" refers to the fate of the planetoid. We also compute the energies and likely durations of a broad sample of collision events, and identify detection strategies at optical and X-ray wavelengths. Collisions with the most massive planetoids can be detected in external galaxies. Some may trigger nuclear burning. If one in $\sim 10^7-10^8$ of WD-planetoid collisions creates the conditions needed for a Type Ia supernova (SN~Ia), "death-by-dynamics" would also refer to the fate of the WD, and could provide a novel channel for the production of SN~Ia. We consider the circumstances under which the rate of SNe~Ia can be increased by interactions with planetoids.