The Diffuse Interstellar Bands

The Diffuse Interstellar Bands (DIBs for short) is the common name for a set of hundreds of absorption lines (see illustration above) that are detected from the near-UV to the near-IR in the spectra of so-called reddened stars - meaning there is a lot of interstellar material between us and the star. The first of these bands was detected as early as 1922, yet as of today, not one singlel ine is identified with a carrier, which makes the DIBs the longest standing problem in astronomical spectroscopy.

We do know that these bands are of interstellar origin, that whatever is causing the bands must be widespread in our galaxy and beyond, must be very stable to withstand the harsh conditions of the interstellar medium and are most likely large carbonaceous free molecules. Candidate carrier molecules include carbon chains, Polycyclic Aromatic Hydrocarbons (PAHs) and fullerene-type compounds.

A final identification of the DIBs will require a match with laboratory data. The problem is that the above mentioned classes of molecules still contain large numbers of molecules, which each have their unique spectrum. For instance, there are about 1.2 million different PAH molecules with less than 100 carbon atoms. Measuring all these molecules in the laboratory would take a lot of time and money. Astronomers therefore try to determine the molecular properties of the DIB carriers from their observations. This eliminates many molecules as potential carriers. The identification of the DIBs will thus be based on astronomical observations, laboratory experiments and theoretical calculations.

My DIB-related research has focused on statistical analyses of DIB properties, ionization properties of the DIB carriers and detailed analyses of the line profiles of certain DIBs. I am also involved in a search for certain specific PAH molecules measured in the gas phase (at the Interstellar Simulation Chamber at the NASA Ames Research Center).