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| Betelgeuse is a red giant in our galaxy. |
Red giant is a short phase in the lifecycle of a star. There is expansion of the outer layers of the star and cooling as the star exhausts the fuel
in the core. Once the fuel for fusion is gone, the balance between pressure and gravity is upset.
The core shrinks. Fusion still occurs in the shell of the star. This occurs so fast that the gasses
surrounding the core are “puffed off.” Because the surface has expanded, the energy is spread out over
a larger area so the surface is “cooler,” giving off a red color. Red giants eject a lot of mass
through “winds.” A Red Giant is large in terms of size, but it has lost atoms so it is less massive!
Our sun will eventually reach the red giant phase and its diameter will expand to the orbit of
Mars.