White dwarf stars are the final stage of stellar evolution for stars with low to medium mass (up to about 8 solar masses). They are very dense, with a mass similar to that of the Sun but a volume only about the size of the Earth. This means that they have a very high surface gravity. The surface temperature of a white dwarf is determined by its mass and radius, and the higher surface gravity of a white dwarf means that it has a higher surface temperature than a red supergiant.
Red supergiants, on the other hand, are massive stars that are in the late stages of their evolution. They are very large and luminous, with a surface temperature that is cooler than that of white dwarf stars.
