Red Giant
A star starts converting into a Red Gaint once the core runs out of hydrogen. As there is no more fuel, the nuclear fusion cease. Without the outward pressure generated from these reactions, there is nothing to act against the force of gravity. The outer layers of the star begin to collapse inward toward the core. Just as during formation, when the material contracts, the temperature and pressure increase. This newly generated heat temporarily counteracts the force of gravity, and the outer layers of the star are now pushed outward. The star expands to larger than it ever was during its lifetime -- a few to about a hundred times bigger. The star has become a red giant.
The Red Gaint has a low mass, immense radius and low surface temperature. As the name suggest the star is a reddy, yellowy colour.
