太陽は現在、水素をコアのヘリウムに融合しており、約46億年にわたってそうしています。コアの水素が枯渇するまで、融合プロセスはさらに50億年ほど続きます。その時点で、コアは収縮して熱くなり、太陽の外層が膨張して冷やされ、太陽が赤い巨人に変わります。

赤い巨大段階では、太陽はヘリウムを炭素や酸素などのより重い元素に融合し始めます。最終的に、コアはヘリウムをネオンやマグネシウムなどのより重い元素に融合するのに十分な高温で密集します。ただし、鉄が最も安定した要素であり、鉄の融合は放出よりも多くのエネルギーを必要とするため、太陽は鉄を生産する要素を融合することはできません。

約50億年後、太陽は燃料をすべて使い果たし、白い小人になります。
The sun is currently fusing hydrogen into helium in its core, and it has been doing so for about 4.6 billion years. The fusion process will continue for another 5 billion years or so, until the hydrogen in the core is depleted. At that point, the core will start to contract and heat up, which will cause the outer layers of the sun to expand and cool, turning the sun into a red giant.

During the red giant phase, the sun will start to fuse helium into heavier elements, such as carbon and oxygen. Eventually, the core will become hot and dense enough to fuse helium into even heavier elements, such as neon and magnesium. However, the sun will never be able to fuse elements to produce iron because iron is the most stable element and fusion of iron requires more energy than it releases.

In about 5 billion years, the sun will exhaust all of its fuel and become a white dwarf, a small, dense, and incredibly hot object that will gradually cool over billions of years.