The space between the stars, the interstellar medium (ISM), is cold and very thin, but not completely empty: two particles collide there on average once every fortnight. So the ISM is not a place where you would expect to find much chemistry. Nevertheless, a lot of things happen there chemically and reactions in the gas phase and on cold icy dust particles provide an amazing chemical diversity.

In the laboratory, astrochemists investigate how these substances can be created in space. ‘We mimic pieces of interstellar space to find out what astrochemical reaction networks look like’, Harold Linnartz, Professor of Laboratory Astrophysics at Leiden University, says. ‘These are the pieces of the puzzle that should give us a picture of the universe as a reaction vessel.’ 

Fullerenes 

Around 250 different molecules have now been discovered in space, small and large, stable and highly reactive. To do this, telescopes such as the Atacama Large Millimetre Array (ALMA) or the Herschel Space Telescope scour the sky for spectral data that correspond to analysed laboratory data. ‘An important class of molecules here are the polycyclic aromatic hydrocarbons or PAHs’, says Linnartz. Such molecules consist of five- and six-ring carbon atoms and are formed when stars eject large amounts of material at the end of their lives, a bit like a glowing cosmic candle.