What key characteristic marks stars found in Globular Clusters as being ancient?
Answer
Their low metallicity, meaning few elements heavier than hydrogen and helium.
A primary indicator used by astronomers to identify stars dating back to the infancy of the galaxy is their chemical composition, specifically their metallicity. Ancient stars formed before multiple generations of massive stars had lived, exploded, and dispersed heavy elements throughout the interstellar medium. Consequently, these primordial stars possess very low metallicity, containing only trace amounts of elements heavier than hydrogen and helium. This chemical fingerprint distinguishes them from younger stars found in regions like the thin disk, which have incorporated material enriched by previous stellar lifecycles.
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