Explanation:
when a main-sequence star exhausts its core hydrogen fuel supply the core starts to shrink ( lack of fusion reactions) and the rest of the star starts to expands. The fusion reaction leaves the main sequence and begin to fuse helium in a shell outside the core. This mass stars become red supergiant and then evolve to become blue super giant.
Answer: Their temperature decreases dramatically, but their luminosity increases only slightly.
Explanation: This is exact from Plato
