What object remains at the center of a planetary nebula providing the energy for its glow?

Answer

A white dwarf (or pre-white dwarf)

After shedding its outer layers, the star's core shrinks and heats significantly, becoming a white dwarf which emits intense, high-energy ultraviolet radiation necessary to illuminate the surrounding gas.

What object remains at the center of a planetary nebula providing the energy for its glow?
astronomystarsnebulaeVisibilityplanetary nebulae