27 October 2011
Stars manufacturing complex organic matter?
by Kate Melville
An analysis of the spectral emissions from distant stars suggests that compounds of unexpected complexity - some resembling coal and petroleum - exist throughout the universe and are being made by stars. The proponents of this controversial idea, Professors Sun Kwok and Yong Zhang of the University of Hong Kong, argue their case in the current issue of the journal Nature.
Kwok and Zhang base their hypothesis on a set of infrared emissions - known as "Unidentified Infrared Emission Features" - previously detected in stars and interstellar space. Since the first recording of these emissions, the most commonly accepted theory regarding their origin has been that they come from simple organic molecules made of carbon and hydrogen atoms, known as polycyclic aromatic hydrocarbons (PAH).
Kwok and Zhang contend, however, that observations from the Infrared Space Observatory and the Spitzer Space Telescope indicate that these spectra have features that cannot be explained by PAH molecules alone. Rather, they propose that the substances generating these spectra have chemical structures that are much more complex. By analyzing the emissions of star dust formed in exploding stars, they claim that stars are making these complex organic compounds in timeframes of only weeks.
The scientists add that not only are stars producing this complex organic matter, they are also ejecting it into interstellar space. "Our work has shown that stars have no problem making complex organic compounds under near-vacuum conditions," said Kwok. "Theoretically, this is impossible, but observationally we can see it happening."
Kwok says that the compounds are so complex that their chemical structures resemble those of coal and petroleum. Coal and oil are thought to arise only from living organisms but the tell-tale spectra, he argues, show complex organic compounds can be synthesized in space even when no life forms are present.
Kwok and Zhang's work raises the possibility that stars enriched the early solar system with complex organic compounds. The early Earth was subjected to bombardment by comets and asteroids, which may have been delivery vehicles for this organic star dust. Whether these organic compounds played any role in the development of life on Earth remains an open question.
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Source: The University of Hong Kong