The star can form a White Dwarf, then a planetary nebula. A White Dwarf is the inert stellar core that remains after a star has ended all core nuclear fusion. All nuclear fusion is over, that is, all available hydrogen in the star’s core has been fused into helium and the helium into carbon. This White Dwarf stellar core is incredibly dense; in fact if you were to weigh a White Dwarf, it would weigh about 5 tons per teaspoon. It is extremely dense due to the collapse of the star’s core; gravity has created an incredible density.