Introduction

Interstellar dust is an important component of the interstellar medium. Dust provides the dominant opacity source in the interstellar medium for non-ionizing photons and therefore controls the spectral energy distribution of the ISM at all wavelengths longer than 912 Å. Dust grains also lock up a substantial fraction of all heavy elements. Grains provide a surface on which species can accrete, meet, and react – giving rise to an interesting and complex chemistry. This chapter will look at the physical processes involving dust, including their interaction with light – in particular their energy balance and the resulting temperature – and their charge balance. Dust also regulates the gas phase abundances of the elements through accretion and destruction processes. This chapter discusses the physical processes involved in dust destruction. The chemical processes that control accretion and ice mantle formation are described in Section 4.2. The growth and characteristics of interstellar ice mantles are discussed in Sections 10.6 and 10.7.4. We will return to the lifecycle of interstellar dust and the depletion of the elements in Chapter 13. The composition of interstellar dust has been widely debated and silicates and graphite are generally considered the most important interstellar dust components. In this chapter, we have therefore focussed on these compounds. However, the discussion is very general and one might often substitute minerals for silicates and amorphous carbon for graphite in the discussion of the physical processes.