In 2004, a team of scientists discovered hydrocarbons called anthracene and pyrene in an amazing structure called the Red Rectangle!
Here two stars 2300 light years from us are spinning around each other while pumping out a huge torus of icy dust grains and hydrocarbon molecules. It’s not really shaped like a rectangle or X—it just looks that way from here. The whole scene is about one third of a light year across.
This was first time such complex molecules had been found in space:
• Uma P. Vijh, Adolf N. Witt, and Karl D. Gordon, Small polycyclic aromatic hydrocarbons in the Red Rectangle, The Astrophysical Journal 619 (2005), 368–378.
Wherever carbon-containing materials suffer incomplete combustion, you get PAHs, or polycyclic aromatic hydrocarbons. In Earth you can find them in soot, or the tarry stuff that forms in a barbecue grill. They’re common in outer space, too.
But what are PAHs like, exactly? They’re made of hexagonal rings of carbon atoms, with some hydrogens along the edges:
Benzene has a single hexagonal ring, with 6 carbons and 6 hydrogens. You’ve probably heard about naphthalene, which is used for mothballs: this consists of two hexagonal rings stuck together. True PAHs have more. With three rings you can make anthracene:
and phenanthrene:
With four, you can make napthacene:
pyrene:
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