There's an unidentified source of infrared throughout the universe. By looking at the specific wavelengths of the light, scientists think that come from carbon - but not just any carbon, a special kind where the atoms are arranged in multiple hexagonal rings. No one has been able to spot one of these multi-ring "polycyclic aromatic hydrocarbons," or PAHs in space - even though the infrared emissions imply that these PAHs should make up 10 per cent of the universe's carbon. Now, scientists have found a new hint.