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A large fraction of white dwarfs are accreting or have recently accretedrocky material from their planetary systems, thereby polluting theiratmospheres with elements heavier than helium. In recent years, the quest formechanisms that can deliver planetesimals to the immediate vicinity of theircentral white dwarfs has stimulated a flurry of modelling efforts. The observedtime evolution of the accretion rates of white dwarfs through their multi-Gyrlifetime is a crucial test for dynamical models of evolved planetary systems.Recent studies of cool white dwarfs samples have identified a significantdecrease of the mass accretion rates of cool, old white dwarfs over Gyrtimescales. Here, we revisit those results using updated white dwarf models andlarger samples of old polluted H- and He-atmosphere white dwarfs. We find nocompelling evidence for a strong decrease of their time-averaged mass accretionrates for cooling times between 1 and 8 Gyrs. Over this period, the massaccretion rates decrease by no more than a factor of the order of 10, which isone order of magnitude smaller than the decay rate found in recent works. Ourresults require mechanisms that can efficiently and consistently deliverplanetesimals inside the Roche radius of white dwarfs over at least 8 Gyrs.

No evidence for a strong decrease of planetesimal accretion in old white dwarfs