What is included in the definition of "metals" according to astronomers when analyzing nebula metallicity?
Everything heavier than helium, such as oxygen, nitrogen, and carbon.
In the context of astrophysics and nebula elemental analysis, the term 'metals' is used as shorthand for any element heavier than hydrogen and helium. Since hydrogen and helium were primarily created during the Big Bang, all subsequent heavier elements—including essential components like oxygen, nitrogen, carbon, neon, and sulfur—are considered metals because they were synthesized later, primarily within previous generations of massive stars and dispersed via events like supernovae. This distribution of heavier elements, termed metallicity, acts as a chemical fingerprint linking the current cloud material to those prior violent stellar deaths, and its presence signals the potential for forming rocky planets.
