1. Main Sequence: Currently, the Sun is in its main sequence stage, where it fuses hydrogen into helium in its core, releasing energy as light and heat. This stage will last for about 10 billion years.
2. Red Giant: As the Sun runs out of hydrogen fuel in its core, it will start to fuse hydrogen in a shell surrounding the core. This causes the Sun to expand and cool, becoming a red giant. It will engulf Mercury and Venus, and likely Earth as well.
3. Helium Flash: Once the core becomes hot enough, helium will begin to fuse into carbon and oxygen, releasing a huge burst of energy known as the helium flash.
4. Horizontal Branch: After the helium flash, the Sun will stabilize and become a horizontal branch star, fusing helium in its core.
5. Asymptotic Giant Branch (AGB): Eventually, helium will also run out in the core, and the Sun will expand again, becoming an AGB star. It will fuse heavier elements in shells around the core.
6. Planetary Nebula: As the Sun sheds its outer layers, it will create a beautiful, expanding shell of gas known as a planetary nebula. This nebula is not related to planets, but is named for its round, planet-like appearance.
7. White Dwarf: Finally, the Sun's core will be left behind as a white dwarf - a dense, hot remnant of the star's former self. It will slowly cool over billions of years, eventually becoming a black dwarf.
So, the Sun will not explode as a supernova, which is the fate of more massive stars. Its eventual demise is a more gradual process, leaving behind a relatively small, but incredibly dense, white dwarf.
