Here's why:
* Helium Fusion: Red giants are stars that have exhausted the hydrogen fuel in their core. They then start fusing helium into carbon and oxygen. This process generates a lot of energy, causing the star to expand significantly.
* Helium Exhaustion: Eventually, the helium in the core gets used up. The core then collapses under its own gravity.
* Formation of a White Dwarf: The collapse of the core triggers a series of events. The outer layers of the star are ejected into space, forming a planetary nebula. The remaining core, now mostly made of carbon and oxygen, is extremely dense and hot. It cools down over time, eventually becoming a white dwarf.
Key Characteristics of a White Dwarf:
* Dense: White dwarfs are incredibly dense, packing the mass of a star into a volume the size of the Earth.
* Hot: They start out very hot, but cool down over billions of years.
* Stable: White dwarfs are stable and don't undergo any further nuclear fusion. They are essentially the "ashes" of a star's life.
Important Note: This process only applies to stars that are smaller than about 8 times the mass of our sun. Larger stars go through a more complex series of events and may end up as neutron stars or black holes.
