DIBs

Diffuse interstellar bands (DIBs) are a series of absorption features observed in the optical and near‑infrared spectra of stars, caused by material in the interstellar medium. Over 400 distinct DIBs have been catalogued, ranging from visible wavelengths around 400 nm to the near‑infrared at 1.5 micrometres. The patterns of these bands vary with the line of sight, providing a probe of the distribution and physical conditions of interstellar dust and gas.

The first DIBs were reported by Heger in 1919, and their identification remained a mystery for many decades. Early theories proposed that the absorption was due to simple molecules or atoms, but subsequent observations ruled out most inorganic species. The complex profiles and broad widths suggested that large carbon‑based molecules were likely responsible. Today the leading candidates include polycyclic aromatic hydrocarbons (PAHs), fullerenes such as C60+, and long carbon chains, though no single carrier has been definitively confirmed for all features.

Astronomers employ high‑resolution spectroscopy to map DIB strengths across the sky. The correlation between DIB intensity and extinction—dust‑related attenuation of starlight—enables the use of DIBs as tracers of interstellar matter where dust is present but not otherwise easily observable. Because DIBs arise from trace constituents, their study offers insight into the chemical complexity of the interstellar medium and the processes that produce and destroy large organic molecules in space. Continued observations with large telescopes and space‑based instruments aim to resolve the remaining ambiguities regarding the precise identities and physical environments of the DIB carriers.