It was recently proposed that metal-rich white dwarfs (WDs) accrete their
metals from compact debris disks found to exist around more than a dozen of
them. At the same time, elemental abundances measured in atmospheres of some
WDs imply vigorous metal accretion at rates up to 1011 g/s, far in excess
of what can be supplied solely by Poynting-Robertson drag acting on such debris
disks. To explain this observation we propose a model, in which rapid transport
of metals from the disk onto the WD naturally results from interaction between
this particulate disk and spatially coexisting disk of metallic gas. The latter
is fed by evaporation of debris particles at the sublimation radius located at
several tens of WD radii. Because of pressure support gaseous disk orbits WD
slower than particulate disk. Resultant azimuthal drift between them at speed
~1 m/s causes aerodynamic drag on the disk of solids and drives inward
migration of its constituent particles. Upon reaching the sublimation radius
particles evaporate, enhancing the density of metallic gaseous disk and leading
to positive feedback. Under favorable circumstances (low viscosity in the disk
of metallic gas and efficient aerodynamic coupling between the disks) system
evolves in a runaway fashion, destroying debris disk on time scale of ∼105 yr, and giving rise to high metal accretion rates up to 1010−1011
g/s, in agreement with observations.Comment: 5 pages, 2 figures, submitted to ApJ