Stars produce energy and light mainly through nuclear fusion in their cores. In main-sequence stars like the Sun, hydrogen nuclei (protons) fuse to form helium through processes such as the proton–proton chain and, in hotter cores, the CNO cycle. This fusion releases a large amount of energy in the form of photons and kinetic energy, which provides the outward pressure that balances gravity and keeps the star stable for most of its life. As fusion progresses and hydrogen runs out, stars evolve and may fuse heavier elements in later stages, ultimately ending their lives in dramatic events like supernovae (for massive stars) or quietly shedding outer layers as white dwarfs (for smaller stars). Key points:
- Core fusion converts hydrogen into helium, releasing energy that powers the star.
- The dominant pathways in sun-like stars are the proton–proton chain and, at higher temperatures, the CNO cycle.
- Fusion energy keeps the star in hydrostatic equilibrium, opposing gravitational collapse.
- Heavier elements are produced in stars over their lifetimes, enriching the cosmos when stars die.
- The specific fusion processes and their contributions depend on the star’s mass and core temperature.
If you’d like, I can tailor this to a particular type of star (for example, the Sun, a massive young star, or a red giant) and explain the dominant fusion stages and observable consequences for each.
