post-main sequence evolution

Post-main sequence evolution describes what happens to a star after it has exhausted the hydrogen fuel in its core. Once the core runs out, the star undergoes changes: it often expands into a giant or supergiant, and its outer layers cool and swell. During this phase, the star may fuse heavier elements, leading to various structures like planetary nebulae or supernovae, depending on its mass. Ultimately, the star expels its outer layers and leaves behind a core remnant—such as a white dwarf, neutron star, or black hole—marking the end of its lifecycle.