Description: The word metal in astronomy is generally used to mean any chemical element except hydrogen or helium. Nucleosynthesis shortly after the Big Bang resulted in a Universe that was almost entirely hydrogen and helium with only trace amounts of other elements. Over time, nuclear fusion in the cores of stars converted some of this hydrogen and helium into heavier elements such as carbon, oxygen, nitrogen, and iron. These new heavier elements were further transformed by slow nuclear reactions inside giant stars and rapid nuclear reactions in supernova explosions and neutron star collisions to form the natural elements we know today. The metal content (called metallicity) of stars increases with each generation of stars. In our Milky Way galaxy, the oldest stars typically have the lowest metallicity.

Related Terms:

• Giant Star
• Milky Way
• Nuclear Fusion
• Supernova
• Big Bang Nucleosynthesis

Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

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