What is the primary source of energy that makes a white dwarf luminous when first formed?

Answer

Residual heat retained from its previous life stages

A newly formed white dwarf is intensely hot because it retains heat from the end stages of its existence; this heat is a residual reservoir, not actively replenished by ongoing nuclear fusion.

What is the primary source of energy that makes a white dwarf luminous when first formed?
stellar evolutionastrophysicsFusionwhite dwarfDegeneracy pressure