Here's what happens:
1. Hydrogen Fuel Depletion: The star runs out of hydrogen fuel in its core, which is where nuclear fusion occurs, producing energy.
2. Core Contraction: Without fusion, the core starts to contract due to gravity.
3. Shell Burning: The core contraction causes the outer layers of the star to expand and cool. The star becomes a red giant. Hydrogen fusion starts in a shell surrounding the core.
4. Helium Flash: Eventually, the core becomes hot enough to ignite helium fusion, which releases a tremendous amount of energy, causing the star to briefly brighten and contract.
5. Further Evolution: After the helium flash, the star will continue to evolve, eventually becoming a white dwarf.
Key Points:
* Lower-mass stars: These are stars with masses less than about 8 times the mass of the Sun.
* Red Giant: A red giant is a large, cool, and luminous star.
* White Dwarf: A white dwarf is a very dense, hot, and small star that has exhausted its nuclear fuel.
Let me know if you have more questions about the life cycle of stars!
