What Happens When Sun Become a Red Giant?
The sun is gradually expanding and in about 5 billion years, it will enter the red giant phase. During this phase, the sun will transition from burning hydrogen in the core to burning hydrogen around the core, which has been converted into helium by hydrogen burning.
This will dramatically increase energy production, causing the star to expand more than 200 times to reach a new equilibrium state. Theoretical modeling and observations, combined with distance determinations from the Gaia spacecraft, suggest that the sun could potentially engulf the Earth when it reaches its maximum size.
Helium burning will begin when the sun reaches the tip of the asymptotic giant branch (AGB). For a star like the sun, helium burning occurs through thermal pulses, resulting in significant mass loss with each pulse, ultimately leading to the sun's demise. However, rest assured that Earth will likely not even exist by the time the sun dies.