A spectrum from the Infrared Space Observatory superimposed on an image of the Orion Nebula where the complex organics are found
Researchers at the University of Hong Kong (HKU) claim to have solved the mystery of “Unidentified Infrared Emission features” that have been detected in stars, interstellar space, and galaxies. For over two decades, the most commonly accepted theory regarding this phenomenon was that these signatures come from polycyclic aromatic hydrocarbon (PAH) molecules - simple organic molecules made of carbon and hydrogen atoms. Now HKU researchers say the substances generating these signatures are actually complex organic compounds that are made naturally by stars and ejected into interstellar space.
The team of Prof. Sun Kwok and Dr. Yong Zhang used observations taken by the Infrared Space Observatory and the Spitzer Space Telescope of stardust formed in exploding stars called novae to show that the astronomical spectra contain a mixture of aromatic (ring-like) and aliphatic (chain-like) components that cannot be explained by PAH molecules.
The researchers say the substances generating these infrared emissions actually have chemical structures that are so complex that their structure resembles those of coal and petroleum. Since coal and petroleum are remnants of ancient life and this type of organic matter was only thought to arise from living organisms, the researchers say this suggests that complex organic compounds can be synthesized in space even when no life forms are present.
Supporting an earlier idea by Kwok that old stars are molecular factories capable of manufacturing organic compounds, they say that not only are stars producing this complex matter on extremely short time scales of weeks, but they are also ejecting it into the general interstellar space in between stars.
"Our work has shown that stars have no problem making complex organic compounds under near-vacuum conditions," says Kwok. "Theoretically, this is impossible, but observationally we can see it happening."