The Internal Constitution of the Stars

The internal constitution of stars consists mainly of hot, ionized gas called plasma, composed of hydrogen and helium. At their centers, nuclear fusion occurs, where hydrogen atoms fuse into helium, releasing enormous energy that powers the star’s brightness and heat. This core is under immense pressure and temperature, creating a balance between gravitational force pulling inward and outward pressure from nuclear reactions. Above the core are layers of progressively cooler and less dense material, including the radiative zone and convective zone, culminating in the star's outer atmosphere or photosphere, which emits the light we see. This structure sustains the star's life cycle and brightness.