Credit: Long Zhao, Ralf I. Kaiser, et al./Nature Astronomy, DOI: 10.1038/s41550-018-0399-y
A reaction pathway that can form a hydrocarbon called pyrene through a chemical method known as hydrogen-abstraction/acetylene-addition, or HACA, is shown at the top. At bottom, some possible steps by which pyrene can form more complex hydrocarbons via HACA (red) or another mechanism (blue) called hydrogen abstraction – vinylacetylene addition (HAVA).