Metallicitás

Metallicity refers to the abundance of chemical elements heavier than hydrogen and helium in a celestial object, such as a star or a galaxy. In astronomy, these heavier elements are collectively termed "metals," even though in chemistry, many of them are not considered metals. The term was coined by astrophysicist Ann Merchant.

The metallicity of a star is a key indicator of its age and the chemical evolution of the universe. Stars are primarily composed of hydrogen and helium, with trace amounts of heavier elements. These heavier elements are forged in the cores of stars through nuclear fusion and are dispersed into interstellar space through stellar winds and supernova explosions. Subsequent generations of stars form from this enriched interstellar medium, thus inheriting a higher metallicity.

Astronomers measure metallicity by analyzing the light emitted or absorbed by celestial objects. Specific spectral lines in the light spectrum correspond to different elements. The strength and presence of these lines reveal the abundance of each element. For instance, a star with strong absorption lines of iron and oxygen is considered to have a higher metallicity than a star with predominantly hydrogen and helium lines.

The metallicity of a galaxy is the average metallicity of its stars. Galaxies with lower metallicity are generally older, while those with higher metallicity are younger or have undergone significant star formation and enrichment processes. Studying metallicity helps astronomers understand the history of star formation, galactic mergers, and the overall chemical enrichment of the cosmos over billions of years.