A red giant star is a dying star in the last stages of stellar evolution. In only a few billion years, our own sun will turn into a red giant star, expand and engulf the inner planets, possibly even Earth. What does the future hold for sun and others like it?

According to a  publication in  nature journal,  Stars are born due to hydrogen, but eventually this supply is depleted. The Sun has used roughly half of its hydrogen supply. When this runs out, in five billion years, the Sun — and, by extension, the rest of the Solar System — will undergo a fundamental change. When only a small amount of hydrogen remains, fusion will continue in a shell around the Sun’s core. This will cause the outer envelope of the Sun to swell to an enormous size. The Sun will then start to rapidly eject its outer envelope into interstellar space. The decreasing mass of the Sun will cause the other planets to move outwards, away from the Sun, to conserve angular momentum. When the last of the envelope is ejected, the Sun’s core will be revealed: a smouldering, Earth-sized white dwarf that will slowly cool for the rest of time.

Nature 585, 354-355 (2020). doi: 10.1038/d41586-020-02555-3