What are Polycyclic Aromatic Hydrocarbons (PAHs)?

Polycyclic Aromatic Hydrocarbons (PAHs) are toxic organic compounds formed during incomplete combustion of coal, oil, gas, and biomass. They are environmental pollutants linked to cancer and found in air, soil, and certain foods.

Context: Recent research shows that certain PAHs (like the indenyl cation, C9H7+) can cool down very quickly after absorbing high-energy light, preventing them from breaking apart. This helps explain why so many PAHs survive in space.

What are PAHs (Polycyclic Aromatic Hydrocarbons)?

Polycyclic Aromatic Hydrocarbons (PAHs) are molecules made entirely of carbon and hydrogen.
They have a special structure: their atoms form multiple interconnected rings, like a honeycomb or chain of hexagons.

Key Facts About PAHs

Found Everywhere: PAHs are found on Earth (for example, in smoke from fires, grilled food, and fossil fuels), but they’re also common in space. Astronomers estimate that PAHs make up about one-fifth of all carbon in interstellar space.
Possible Origins of Life: Some scientists believe that PAHs arrived on Earth via meteors, possibly helping create the first building blocks of life. Their ability to survive harsh space environments adds to this theory.
Interstellar Survivors: In places like the Taurus Molecular Cloud 1 (TMC1) — a vast, cold region of gas and dust in space — PAHs are found in larger quantities than expected, even though they are exposed to strong starlight that can break molecules apart.
Molecular Structure: PAHs can be “open-shell” or “closed-shell.” This describes how their electrons are arranged. Closed-shell PAHs have electrons paired up, which can affect how they handle energy.
Why They Matter in Space: PAHs are important in space chemistry. Their survival and growth help spread carbon — a key ingredient for life — to planets and comets.