Why do stars shine for billions of years?
Quick Answer
Stars shine because nuclear fusion in their cores converts mass into energy. Because the process is extremely efficient and only a small amount of mass is fused each second, stars can last for billions of years.
The Full Story
In stars like the Sun, pressure and temperature in the core are high enough for hydrogen nuclei to fuse into helium. A tiny amount of mass is converted into energy according to Einstein’s equation E = mc², and that energy slowly escapes as light and heat. Because the Sun is huge, it contains enough fuel to keep shining for about 10 billion years in total, and it is roughly 4.6 billion years old now. More massive stars burn through their fuel much faster, while smaller stars can last far longer. Stellar lifetimes are therefore controlled by mass and fusion rate.
Key Facts
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