Stellar evolution

Stellar evolution is the process by which a star changes over millions or billions of years, driven by the nuclear fusion reactions in its core. Stars are born from collapsing clouds of gas and dust, gradually heat up until hydrogen fuses into helium, and eventually exhaust their fuel and die—transforming into white dwarfs, neutron stars, or black holes.

A star's life cycle depends primarily on its mass. Massive stars burn through fuel rapidly and live only millions of years, while low-mass stars like our Sun endure for billions. Astronomers map this journey using the Hertzsprung-Russell diagram, which plots stellar brightness against temperature and reveals distinct evolutionary stages.

The process begins with a star spending most of its lifetime in the "main sequence," steadily converting hydrogen to helium. When the core hydrogen is exhausted, the star expands into a red giant, fusing hydrogen in a shell around an inert core. Eventually, the core becomes hot enough to fuse helium, leading to further expansions and contractions. The star's final fate—whether it sheds its outer layers as a planetary nebula or explodes catastrophically as a supernova—depends on whether it has enough mass to collapse.

Understanding stellar evolution helps us grasp the universe's history and the origins of chemical elements.

Related

Stellar nucleosynthesis, Hertzsprung-Russell diagram, Star formation, Astrophysics, Sun, Stellar classification