White dwarf pollution, a journey from 10^5 to 10^(-5) AU

Elements heavier than Helium are expected to sink quickly on white dwarf atmospheres yet are observed on up to 50% of white dwarfs, indicating that these stars are accreting materials from their evolved planetary system. In this talk, I will present simulation results showing the sustained pollution of white dwarfs over Gyr timescales from exo-Oort cloud objects. I will discuss the rich gravitational dynamics driving these bodies to high eccentricities through the interplay of the Galactic tide and a companion star or planet. Then, I will present a model for the accretion process around magnetic white dwarfs. I will show that the star’s magnetic field shapes pollution geometry, leading to white dwarfs with “spotty” metal patches, as recently observed. The existence of these metal patches on observed white dwarfs implies some degree of convective suppression. In addition, metal patches on white dwarfs can affect the inferred accretion rate by several orders of magnitude, affecting many proposed delivery mechanisms.