Fate Of Our Sun - Once It Will Use All Of Its Fuel

Once a star reaches the main sequence phase it stays in this phase as long as it has hydrogen in its core to fuse into helium. Approximately 90% of the lifetime spent by all the stars in the main sequence phase. Stars generate very stable energy during this phase.   

Once all the hydrogen in the core is burnt out , the star evolves rapidly off the main sequence phase and become cooler and more luminous star for rest of its life. The exact fate depends upon the original mass of the star. The next phase is known as the Red Giant Phase. 

Once all the hydrogen is used up, the core is left with all inert Helium Gas. Fusion at the core stops and the gravity at core starts to win again and core start to shrink as a result and heats up. Still there is some hydrogen left in the shell surrounding the core which produces much more energy as compared to main sequence phase. As a result the out shells start to expand.  When Sun will enter this phase after 5 billions years it will expand such that it will swallow Earth inside it. It will grow 100 times in size and 2000 times more hotter. There is no natural thermostat and no equilibrium anymore.

So after 5 billion years once Sun will enter into Red Giant Phase, it will expand outwards and swallow Mercury, Venus and Earth inside it. In other words there will be end to the Planet Earth. Hence the fate of Earth is Written that it will be swallowed by The Sun.

Links to my previous posts on The Story of a Star are given below

https://steemit.com/science/@mathworksheets/story-of-a-star-in-the-womb-of-a-nebula

https://steemit.com/science/@mathworksheets/a-star-story-forming-the-protostar

https://steemit.com/science/@mathworksheets/story-of-a-star-a-brown-dwarf

The Star Story Still Continues......