Here at UCL we have a large group of people interested in astrochemistry — the study of atoms and molecules in space, particularly their formation and destruction. There are only a few groups in the UK that specialise in this field, and the group at UCL is one of the most prolific, looking at astrochemistry from observational, theoretical and even experimental angles.
Astrochemistry is a relatively young field: the first molecule discovered in space was CH, back in 1937, but the subject only boomed in the 1970s and 1980s when advances in technology meant that the submillimetre window through the atmosphere became readily available [see Fig. 1: The Rise of Molecular Complexity].
Fig 1. The Rise of Molecular Complexity.
As technology and our understanding of astrochemistry has developed, our knowledge of the molecular universe has also increased.
Now we have detected about 175 molecules in space, ranging from small, common molecules like CO (carbon monoxide), H2O (water), HCN (hydrogen cyanide) through to “large”, “complex” molecules (by astrochemical standards) like HC11N (a long carbon chain) and C6H6 (the cyclic, aromatic molecule, benzene). In the last couple of years we’ve been amazed by discoveries of huge molecules: C60 and C70, 3D carbon cages reminiscent of footballs or geodesic domes.
I’m currently involved in a large project to look at a family of complex molecules with the formula C2H4O2. This is a family of three isomers (different structural arrangements), which are named methyl formate (HCOOCH3), glycolaldehyde (CH2OHCHO) and acetic acid (CH3COOH). The middle member is particularly interesting to us, since it is relatively rare, but has the interesting property that it leads to prebiotic molecules… molecules which are connected to life. Professor Serena Viti was involved in the discovery of glycolaldehyde (a simple sugar) in a high-mass star-forming region several years ago, and since then we have been investigating how such a complex organic molecule could be formed in space. Only a few months ago, some other researchers reported the detection of glycolaldehyde in a low-mass star-forming region — a region which will give birth to solar-type stars. So this field is of particular current interest.
Our studies show that the keys to the formation of glycolaldehyde are the surfaces of solid particles in space, particles that astronomers call “dust”. In the cold regions where stars begin to form, interstellar gases can freeze onto the surface of these dust grains, in much the same way as frost will form on fallen leaves on a cold winter’s morning. These surfaces reduce the energies needed for complex molecules to form — they catalyse the reactions. It is only in this way that many of the complex molecules we find in star-forming regions can form efficiently. Recently we published a research paper looking at possible chemical routes to the formation of glycolaldehyde. It seems clear that it cannot form from gaseous material; reactions are just too slow in the cold temperatures of space. Of the mechanisms catalysed by dust grain surfaces, we identified a couple of strong possibilities, based on the predicted abundance of available reactants and other chemical and physical considerations. We did this via a computer simulation which ties together a network of thousands of interacting chemical reactions — this is really the only way which we can recreate the conditions of space, since we can’t go there ourselves to do experiments. It is a very successful technique for explaining chemistry throughout the universe.
So now we’re very close to understanding how sugar can form in the depths of space. Since we’ve narrowed it down to a couple of possible pathways, we can move to the vacuum chambers of the UCL chemical laboratories to discover which is the mechanism that dominates. In comparison to computer simulations, experiments are long, difficult and expensive, but they are a useful validation of computer simulations. Stay tuned for further updates in the story of the sweet Cosmos.
– Dr. Paul M. Woods