Detection of two interstellar absorption bands coincident with spectral features of C60+

MORE than a hundred well-defined absorption bands, arising from diffuse gas in the interstellar medium, have been observed in the visible and near-infrared spectra of stars ^1-4. The identity of the species responsible for these bands has remained unclear, although many possibilities have been suggested^5,6. Carbon-based molecules ubiquitous in the interstellar medium have been widely favoured as potential carriers of some of the diffuse interstellar bands^7-10,29 in particular, C₆₀⁺ has been thought to be a promising candidate^9,29. Here we present the results of a search for C₆₀⁺ in the near-infrared spectra of seven stars, based on recent laboratory measurements of the absorption spectrum of this species^11-13. We find two diffuse bands that are coincident (within 0.1%) with laboratory measurements on C₆₀⁺ in a Ne matrix¹¹. From this observation and the total absorption, we estimate that 0.3-0.9% of interstellar carbon is in the form of C₆₀⁺. The molecule is very stable, which should allow it to survive in the interstellar medium for a long time¹⁴, but the inhibition of C₆₀⁺ formation by hydrogen probably limits its abundance.