Andrea Gebek

Galaxies like our own Milky Way constantly evolve due to the interplay of the stars, the gas between the stars (the “interstellar medium”) and the galactic environment. Massive stars at the end of their lifetime explode violently and eject their synthesized elements like oxygen and iron into space, and newborn stars are formed out of this enriched gas. This stellar life cycle leads to younger stars being enriched in metals (note that astrophysicists have the weird convention of classifying all elements except hydrogen and helium as metals). Put another way, the galactic metal abundance generally increases over time. However, this doesn’t happen exactly the same way for all metals. Oxygen, for instance, is mostly produced by very massive stars which have a short lifetime (of the order of ten million years, which is short compared to the lifetime of the sun of ten billion years), while iron is mostly produced in a more complex process which requires a white dwarf – a stellar remnant which emerges not before hundred million years passed.