1. Red Giant Phase:
* Hydrogen Fuel Depletion: The Sun's core will run out of hydrogen fuel, the source of its energy production.
* Core Contraction: Without the outward pressure from nuclear fusion, the core will contract under its own gravity.
* Shell Burning: The core's contraction will heat up the surrounding layers, causing hydrogen fusion to begin in a shell around the core.
* Expansion: The increased energy output will cause the Sun to expand dramatically, becoming a red giant. Its surface will extend beyond Earth's orbit.
2. Helium Flash and Horizontal Branch:
* Helium Fusion: The core will continue to contract until it becomes hot enough to fuse helium into carbon and oxygen. This process is called the "helium flash."
* Horizontal Branch: After the flash, the Sun will settle on the horizontal branch of the Hertzsprung-Russell diagram, a region populated by stars fusing helium in their cores.
3. Asymptotic Giant Branch:
* Helium Depletion: The Sun will eventually run out of helium fuel in its core.
* Second Expansion: The core will contract again, and the Sun will expand even further, becoming an asymptotic giant branch (AGB) star.
* Thermal Pulses: The Sun will experience a series of thermal pulses, brief periods of increased energy production as helium fusion ignites in shells surrounding the core.
4. Planetary Nebula and White Dwarf:
* Mass Loss: During the AGB phase, the Sun will lose a significant portion of its mass through strong stellar winds.
* Planetary Nebula: As the outer layers are ejected, they will form a colorful cloud called a planetary nebula. (Note: This has nothing to do with planets, just the appearance of the nebula through telescopes.)
* White Dwarf: The remaining core, now composed mostly of carbon and oxygen, will shrink into a hot, dense white dwarf. This will be the final stage of the Sun's life.
Timeline:
* Red Giant Phase: About 5 billion years from now
* Helium Flash and Horizontal Branch: About 7 billion years from now
* Asymptotic Giant Branch: About 8 billion years from now
* Planetary Nebula and White Dwarf: About 10 billion years from now
Important Note: The Sun will never become a supernova. Supernovae are only possible for much more massive stars.
Let me know if you'd like more detail on any of these stages!
