Red supergiants (RSGs) are colossal stars, hundreds of times larger than the Sun, wrapped in a cloud of gas and dust. Inside this envelope a real chemical factory works: oxygen is plentiful, fostering molecules like CO, SiO, HCN and H₂O at abundances of about one part per million‑billion of hydrogen. The most striking feature is the turbulence. RSGs lose mass erratically, forming knots, clumps and arcs that race at supersonic speeds. These shocks shatter dust grains and trigger unusual reactions, producing exotic molecules such as AlO, AlOH, PO, TiO₂ and VO in much lower amounts (10⁻⁹‑10⁻⁷ relative to H₂).
Two stars, VY Canis Majoris and NML Cygni, are the most chemically complex laboratories: astronomers have identified over 29 molecular species in their surroundings. Moreover, RSGs emit masers – natural lasers – in OH, H₂O and SiO, which help map the envelope’s structure. Isotope studies reveal that some material originates from deeper stellar layers where hydrogen burning occurs. In short, red supergiants are cosmic labs where chemistry meets violent stellar winds, creating a mosaic of molecules that scientists are still decoding.
