Dust Evolution in the Interstellar Medium
Dust originates in near-stellar regions and is ejected into interstellar space. However, near-stellar dust is not the same as interstellar dust, because various processes operating in the interstellar medium tend to modify the physical and chemical nature of dust. Thus, dust evolves in interstellar space. In hot post-shock gas, dust grains may be shattered or even vaporized in grain–grain collisions, and eroded in gas–grain impacts. These destructive processes can be opposed by grain growth in cooler, denser regions of interstellar space. Starlight can modify the physical and chemical nature of some forms of dust. Higher temperatures tend to promote the conversion of amorphous material to crystalline, while fast particles in the form of cosmic rays tend to drive the reverse transition.