The short-lived radioactive nuclide 26Al was synthesised in either a Red Giant star or a supernova event shortly prior to formation of our solar system.
Anomalous 26Mg resulting from radioactive decay of the short-lived nuclide 26Al is preserved in some early-formed Al-rich meteorite inclusions, indicating that 26Al was synthesised probably during a supernova event immediately prior to formation of our solar system.
26Al is also formed in the Earth’s upper atmosphere by spallation reactions with cosmic rays.
Classic nucleosynthesis theory has 26Al created during explosive carbon burning in a supernova envelope, with a production ratio of 26Al/27Al of ~10-3. Supernovae are astronometically quite rare, so its difficult to explain the high abundance of 26Al observed by spectral studies of our galaxy. However, recent theory suggests that 26Al can also be generated in Red Giant Stars. Presently, the stellar source of the short-lived decay products observed in early-formed solar system meteorites is contentious. However, some (e.g. 182Hf) can’t be synthesised by AGB stars and can only have been synthesised in a supernova event.