Before the Planetary Nebula:
* Red Giant Phase: The star has exhausted the hydrogen fuel in its core, causing it to expand and cool, becoming a red giant.
* Helium Burning: The core contracts and heats up, eventually becoming hot enough to fuse helium into carbon and oxygen.
The Planetary Nebula Formation:
* Core Instability: The core eventually runs out of helium fuel and begins to shrink again. This contraction causes the core to become extremely hot and unstable.
* Shell Burning: The outer layers of the star, which are still primarily hydrogen, begin to burn rapidly in a shell around the core.
* Mass Loss: The intense heat from the shell burning pushes the outer layers of the star outwards, creating a strong stellar wind. This wind carries away vast amounts of material into space.
* Planetary Nebula: The ejected material forms a beautiful, glowing shell called a planetary nebula, which is often shaped by the star's magnetic field.
The White Dwarf Core:
* Contraction: The remaining core, now composed of carbon and oxygen, continues to contract and cool. It is incredibly dense, about the size of the Earth but containing the mass of the Sun.
* White Dwarf: This dense, hot core becomes a white dwarf, a stellar remnant that no longer generates its own energy through fusion.
Key Takeaway: The core of a star does not explode in a supernova when it forms a planetary nebula. It undergoes a relatively peaceful contraction and cooling process, leaving behind a white dwarf.
