Bounding destruction timescales of minor planets orbiting white dwarfs with the sesquinary catastrophe

Abstract

Dynamical activity attributed to the destruction of minor planets orbiting white dwarfs has now been photometrically monitored in individual systems for up to one decade, long enough to measure significant cessation and re-emergence of transit features. Further, periodicities which hint at the presence of debris orbiting exterior to the white dwarf Roche radius, along with widely varying estimates for debris disc lifetimes (up to Myrs), complicate theories for the formation and dynamical evolution of these systems. Here, we illustrate that minor planets orbiting white dwarfs with periods of $\approx$5-25 hours and longer while completely or partially avoiding tidal disruption satisfy the conditions for the occurrence of the sesquinary catastrophe, a phenomenon that occurs in the solar system when impacts from returning ejecta from a moon are fast enough to be erosional to the point of destruction. We hence find that the region corresponding to $\approx$1-4 white dwarf rubble-pile Roche radii represents a danger zone where the collisional timescale for the sesquinary catastrophe to occur is $\sim 10^2-10^5$ yr, suggesting that debris discs around white dwarfs are in a state of semi-continuous replenishment.