* Giant Stars and Nuclear Fusion: Giant stars are formed when stars like our Sun exhaust their hydrogen fuel in their core. This causes the core to contract and heat up, triggering the fusion of helium into heavier elements like carbon. This process causes the star to expand significantly, becoming a red giant.
* Low-Mass Stars and Helium Fusion: Low-mass stars, typically less than half the mass of our Sun, never reach the temperatures necessary to fuse helium. They are simply not massive enough for the core pressure to overcome the electron degeneracy pressure, a quantum effect that prevents further contraction.
* Red Dwarfs: Low-mass stars spend their entire lives fusing hydrogen into helium in their core, slowly becoming cooler and redder. They are known as red dwarfs and are expected to have lifespans of trillions of years, much longer than the age of the universe.
In summary: While larger stars evolve into giants, low-mass stars like red dwarfs never reach the necessary conditions for helium fusion. They stay relatively small and cool throughout their extremely long lives.
