Astronomers Crack Spectral Mystery

Researchers might have nailed down the first identification of a molecule in the sea of compounds that permeate diffuse interstellar clouds and that have mystified scientists for decades. John P. Maier of the University of Basel, in Switzerland, and colleagues report in a paper to be published in an upcoming issue of the Astrophysical Journal that several important absorption lines in dense, complicated interstellar spectra match laboratory-generated gas spectra of a surprisingly simple linear molecule: propadienylidene, H₂C=C=C. Although these so-called diffuse interstellar bands were discovered 90 years ago, astronomers have yet to identify any of the molecules that cause them. Scientists have proposed that complex molecules such as polycyclic aromatic hydrocarbons are largely responsible for the bands. Propadienylidene has also been observed in dense interstellar clouds, so its existence in the diffuse clouds, which are the source of the bands, is plausible. “One could imagine an interstellar synthesis of this species from other molecules that have been observed in diffuse interstellar clouds,” notes astrochemist Benjamin J. McCall of the University of Illinois, Urbana-Champaign. Further research will be needed to make the identification airtight, McCall adds, but the methods for doing so should be straightforward.