Final answer:
The Sun creates energy via nuclear fusion, converting mass into energy as per Einstein's E = mc², allowing it to shine for billions of years.
Step-by-step explanation:
The Sun, like other stars, generates vast amounts of energy through a process called nuclear fusion, where hydrogen atoms fuse to form helium, releasing an immense amount of energy. Every second approximately 600 million tons of hydrogen undergo this reaction in the Sun, with around 4 million tons being converted into energy. Einstein's E = mc² equation explains that mass can be converted into energy, which is how the Sun radiates the energy equivalent of 4 million tons of matter each second.
Despite this massive consumption, the Sun contains enough mass to continue burning at its current rate for billions of years. This nuclear fusion process makes the Sun and other stars incredibly bright and capable of emitting energy continuously over their lifespan.