Diffuse interstellar bands
Diffuse interstellar bands (DIBs) are absorption features seen in the spectra of astronomical objects in the Milky Way and other galaxies. They are caused by the absorption of light by the interstellar medium. Circa 500 bands have now been seen, in ultraviolet, visible and infrared wavelengths.
The origin of DIBs was unknown and disputed for many years, and the DIBs were long believed to be due to polycyclic aromatic hydrocarbons and other large carbon-bearing molecules. Their rapid and efficient deactivation when photoexcited accounts for their remarkable photostability and therefore possible abundance in the interstellar medium. However, no agreement of the bands could be found with laboratory measurements or with theoretical calculations until July 2015, when the group of John Maier (University of Basel) announced the unequivocal assignment of two lines for C60+, confirming a prediction made in 1987.
Much astronomical work relies on the study of spectra - the light from astronomical objects dispersed using a prism or, more usually, a diffraction grating. A typical stellar spectrum will consist of a continuum, containing absorption lines, each of which is attributed to a particular atomic energy level transition in the atmosphere of the star.
All astronomical objects are affected by extinction, the absorption of photons by the interstellar medium. Interstellar absorption predominantly affects the whole spectrum in a continuous way, rather than causing absorption lines, but in 1922 astronomer Mary Lea Heger first observed a number of line-like absorption features which seemed to be interstellar in origin.
...
Wikipedia