Researchers have released a study saying that innumerable small molecules that plunge quietly through the desolate regions of interstellar space make up a major quantity of all carbon, hydrogen, silicon, and other atoms of the universe.
A number of astronomers hypothesize that these interstellar molecules are also responsible for a "diffuse interstellar bands" on Earth, spectrographic proof that something out there in the universe is absorbing certain distinct colors of light from stars before it reaches the Earth, according to an American Institute of Physics press release.
Since we don't know the exact chemical composition and atomic arrangements of these mysterious molecules, it remains unproven whether they are responsible for the diffuse interstellar bands.
Now in a paper published in The Journal of Chemical Physics, a group of scientists led by researchers at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. have offered a new theory: these mysterious molecules may be silicon-capped hydrocarbons like SiC3H, SiC4H and SiC5H.
"There have been a number of explanations over the years, and they cover the gamut," said Michael McCarthy a senior physicist at the Harvard-Smithsonian Center for Astrophysics who led the study, according to the release.
Astronomers have known for a long time that that interstellar molecules containing carbon atoms exist and that they will absorb light shining on them from stars and other luminous bodies.
With that in mind, a number of scientists previously proposed that some type of interstellar molecules are the source of diffuse interstellar bands, which are hundreds of dark absorption lines seen in color spectrograms taken from Earth, according to the release.
Missing colors correspond to photons of given wavelengths that were absorbed as they travelled through the vast reaches of space before reaching Earth, according to the study. The wavelengths reveal the precise energies it took to excite the electronic structures of those absorbing molecules in a defined way if these photons were filtered by falling on space-based molecules.
By demonstrating which molecules in the laboratory have the same absorptive "fingerprints," scientists should be able to use spectroscopy to classify those interstellar molecules.
"Not a single one has been definitively assigned to a specific molecule," said Neil Reilly, a former postdoctoral fellow at Harvard-Smithsonian Center for Astrophysics and a co-author of the new paper, according to the release.
Now McCarthy, Reilly, and their colleagues are pointing to an unusual set of molecules, silicon-terminated carbon chain radicals, as a possible source of these bands.
The team first created silicon-containing carbon chains SiC3H, SiC4H and SiC5H in the laboratory using a jet-cooled silane-acetylene discharge, as mentioned in their paper.
Then they analyzed their spectra and carried out theoretical calculations to determine that longer chains in this family might account for some portion of the diffuse interstellar bands, according to the release.
McCarthy mentioned that the work has not revealed the source of the diffuse interstellar bands yet however. To prove that these silicon capped hydrocarbon molecules are such a source, more work needs to be done in the lab to define the exact types of transitions that these molecules go through.
The study does provide a tantalizing possibility for find the source of some of the mystery absorption bands, and shows more of the rich molecular diversity of space.
"The interstellar medium is a fascinating environment," McCarthy said. "Many of the things that are quite abundant there are really unknown on Earth."
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