PHYSICS A LEVEL Explain why, when a red giant becomes a white dwarf, it moves towards the lower left of the Hertzsprung-Russell diagram [2]

The fusing red giant shell drifts away form the core forming planetary nebula. Leaving only very hot core (white dwarf) (1) The core is hotter than the shell , the star moves left on the diagram. (1) Luminosity decreases because the only emitted photons are formed in earlier stages of evolution and therefore have less energy (1)