All stars die, but not all stars “explode.” A supernova is a violent explosion that marks the end of a star’s life cycle. But our sun, the most famous star in our sky, is destined for a gentler death.
Astronomers estimate that in approximately five billion years, the sun will begin to die when its core runs out of hydrogen, its primary fuel source. As the core collapses, temperatures will increase until helium starts burning into carbon. In the shell around the core, the rising temperature will cause hydrogen nuclei to combine into more massive helium nuclei.
Gaining energy from this nuclear fusion in its shell, the sun’s outer layers will expand. As the outer layers get further away from the energy source, their temperature will decrease. At this point, the sun will be a red giant – a relatively cool star with a surface temperature of approximately 3500K, still large enough to envelop the current orbits of Earth and Mars.
However, the sun is not sufficiently massive to explode in a type II supernova, which requires at least eight solar masses. Instead, the core will turn into a white dwarf, a small, dense stellar remnant that slowly cools down while shining. Meanwhile, the sun’s outer layers will turn into a cloud of dust and gas that gradually drifts off into space.
Our sun’s final exit, therefore,will be surprisingly undramatic. While more massive stars go out with a bang, the centerpiece of our solar system will go out with a sigh.