Interstellar carbon dust

Abstract

Carbon is the fourth most abundant element in the Universe after hydrogen, helium and oxygen. Synthesized at the late evolutionary stage of stars, carbon is ejected from stars through mass loss of asymptotic giant branch stars and explosion of supernovae and then enters the interstellar medium in the form of ions, atoms, molecules and solid dust particles. Carbon-containing complex organic molecules are essential for the origins of life, and carbonaceous dust is a major component of interstellar grains whose infrared absorption and emission spectra provide a powerful diagnosis of the physical and chemical conditions of astrophysical regions where the dust is found. Carbonaceous dust materials such as graphite, nanodiamonds, polycyclic aromatic hydrocarbon molecules, fullerene, and hydrogenated amorphous carbon are ubiquitously present in the interstellar space and are the most promising candidate carriers of the unidentified 2175 A extinction bump, the unidentified infrared emission bands at 3.3, 6.2, 7.7, 8.6, and 11.3 µm, and the mysterious diffuse interstellar absorption bands. Here we focus on the observational properties of interstellar carbonaceous grains and their physical and chemical characteristics. Also discussed are graphene and carbon nanotubes which may be present in the interstellar space.