Answer:
Fusion
Explanation:
The thermonuclear fusion(only occurs at extreme conditions of temperature and pressure like interiors of stars) of Hydrogen takes place in The Sun's core.
Every four hydrogen atoms combine to form a Helium atom with a release of 26.7Mev of energy.
On a large scale this amount of energy can be very huge.
It is calculated that tis proces has being going on for the past [tex]5\times[/tex] [tex]10^{9}[/tex] years and with the amount of Hydrogen left will be sufficient to keep it going for the same amount of time in the future.
After this process ends,the Sun's core which will be mostly Helium,will start to cool and collapse under its own gravity.
