The Destruction of Interstellar Dust

Abstract

This paper reviews the detailed physics of the processes involved in the destruction of interstellar dust in interstellar shocks: sputtering by impacting gas atoms, and vaporization and shattering by grain-grain collisions. An analytical formalism is developed that describes these processes. The structure of interstellar shocks is discussed and the fate of grains in the cooling postshock gas is followed. Theoretical calculations show that high velocity shocks (υ > 50 km/s) destroy interstellar dust efficiently. A simple stick model for evolution of interstellar dust in the interstellar medium (ISM), which includes dust destruction by shocks in the Warm ISM, accretion in the cloud phases, Stardust injection, and mixing between the interstellar cloud and intercloud phases is described. It is concluded that fast shocks occur so frequently that the lifetime of refractory grains such as graphite and silicates is only 5 × 108 yr, much shorter than the Stardust injection timescale. Consequently, growth of interstellar dust through accretion in the cloud phases of the ISM has to be rapid as well. This model is also used to derive rather directly dust lifetimes against destruction and accretion timescales from observations of depletions in the cloud and intercloud phases of the ISM. These are compared to the theoretically calculated lifetimes and the implications are discussed.