What is the defining characteristic of the red giant phase, paradoxically?
Answer
The cooling of its outer layers
The defining feature of the red giant phase is the cooling of the outer stellar layers, even though the star produces much more total energy. This cooling occurs because the energy is spread over a vastly larger surface area.

#Videos
What Causes a Red Giant's Surface to Cool? - YouTube
Related Questions
What is the defining characteristic of the red giant phase, paradoxically?What event triggers the heating of the hydrogen shell surrounding the core in a star that has exhausted its core hydrogen?What physical principle directly causes the surface temperature of the expanding giant to drop?In the relationship $L ext{ propto } R^2 T^4$, what factor dominates the luminosity increase when a star transitions from main sequence to red giant?If our Sun becomes a red giant, to what extent might its radius increase?Which spectral class would the Sun likely move into upon becoming a red giant?What process characterizes the energy generation during the stable main sequence phase?How is the visible color shift to red explained during the red giant phase?What is the ultimate remnant left behind after a Sun-like star exhausts its fuel supply at the end of the giant phase?What is the primary physical reason a red giant is significantly brighter than it was during its main-sequence life?