How are panatery Nebula formed and when do they die

[ehabmozart]

My simple question is how are panatery nebula formed.. Al what i know is that after helium fusion is over, some complex process will occur leading to explosion which leads to the nebula... What are these complex processes...Moreover, it appears just like a core of a star surrounded by some dust... And how to they ultimately end becoming a white dwarf?? Thanks in advance... I need answers urgently

 

[manojr]

For quick overview, see Wikipedia articles on R-process and White dwarf.