  The infrared dust emission from the white dwarf GD 56 is found to rise and
fall by 20% peak-to-peak over 11.2 yr, and is consistent with ongoing dust
production and depletion. It is hypothesized that the dust is produced via
collisions associated with an evolving dust disk, temporarily increasing the
emitting surface of warm debris, and is subsequently destroyed or assimilated
within a few years. The variations are consistent with debris that does not
change temperature, indicating that dust is produced and depleted within a
fixed range of orbital radii. Gas produced in collisions may rapidly
re-condense onto grains, or may accrete onto the white dwarf surface on viscous
timescales that are considerably longer than Poynting-Robertson drag for
micron-sized dust. This potential delay in mass accretion rate change is
consistent with multi-epoch spectra of the unchanging Ca II and Mg II
absorption features in GD 56 over 15 yr, although the sampling is sparse.
Overall these results indicate that collisions are likely to be the source of
dust and gas, either inferred or observed, orbiting most or all polluted white
dwarfs.
