Cracking the puzzle of unusual molecules in deep space that absorb some wavelengths of starlight is like unlocking the secrets of the Rosetta Stone, according to Rob Sharp of the Australian National University’s Research School of Astronomy and Astrophysics. “It’s the longest-standing problem in astronomical spectroscopy,” he says.

The identity of the molecules has been a mystery for 80 years, but Rob has now joined forces with chemists at the University of Sydney to try to crack the molecular code.

The best clues could lie in a bizarre object called the Red Rectangle, a tightly shaped gas cloud surrounding what is probably a dying binary star system. This nebula is an unusual red colour, which is probably caused by the mystery molecules.

The key suspects are polycyclic aromatic hydrocarbons (PAHs), giant constructs of carbon and other elements. But “we can’t get some key information from our wavelength absorption observations,” says Rob, “so my chemistry colleagues are testing gas mixtures under controlled conditions in the laser laboratory to give us the missing information about these important molecules.”

Rob and his team then use that data to investigate what they see in the light spectrum. “These PAHs are basically combustion by-products of stellar evolution,” says Rob. “They’re complex molecules and we don’t yet understand their formation mechanisms in space. And if we want to understand the evolution of stars and galaxies, we need to comprehend the overall chemical picture.”

PHOTO: THE RED RECTANGLE IS A PECULIAR NEBULA WITH SOME STRANGE CHEMICAL PROPERTIES. CREDIT: NASA/ESA/ HANS VAN WINCKEL (CATHOLIC UNIVERSITY OF LEUVEN) /MARTIN COHEN (UCB).

Research School of Astronomy and Astrophysics, Australian National University, Canberra
Dr Rob Sharp, Tel: +61 (2) 6125 0233, rgs@mso.anu.edu.au, rsaa.anu.edu.au/