The Diffuse Interstellar Bands (DIBs) are a group of many broad absorption bands mainly in the visible first observed by A.J.Cannon more than 100 years ago. D.G.York at the University of Chicago leads a team of 10 DIBs astronomers to which I belong. We have observed ~500 DIBs toward ~300 stars in all directions of the sky. They demonstrate the ubiquitous presence of an enormous amount of large organic molecules in interstellar space. A sizable fraction of carbon atoms in the Universe are locked up in the carriers of DIBs. Many astronomers and spectroscopists speculated on the identity of the carriers of DIBs only to fail. Two years ago, after many years of systematic laboratory investigations, J.P.Maier demonstrated that two (later 5) lines of C60+ match with DIBs. This was initially speculated by B.H.Foing and P.Ehrenfreund in 1994 based on Maier’s 1993 matrix spectrum but it took Maier 22 years to obtain the spectrum of gaseous C60+ at the low temperature of interstellar space. If C60+ explains 5 spectral lines, there need to be ~100 organic molecules to cause the observed 500 lines. Candidates are fulleranes, PAHs, and carbon chains. I favor carbon chains although many have been already tested by Maier. The Extended Tails toward Red we discovered in the sightline of the star Herschel 36 are best explained by medium size polar carbon chain molecules (Oka et al. 2013). So is the very characteristic 5797 DIB observed toward ζ Ophiuchus (Huang & Oka 2015). In view of the low temperature and low density of the diffuse interstellar medium, it seems highly unlikely that those large carbon molecules are produced bottom up from atoms and simple molecules as in dense clouds. They must be produced top down from decomposition of dust by cosmic rays, shocks, and VUV photons.

Diffuse interstellar bands: 100-years-old mystery beginning to be solved

254th National Meeting (2017)

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