THE FUTURE OF OUR STAR
Astronomers predict the future of the Sun by looking at what has happened to similar stars. Its life is now about half over. As it consumes hydrogen in its core, leaving an "ash" of helium behind, the Sun will grow hotter and brighter.
When its hydrogen begins to run low, about five billion years from now, the Sun will grow into a red giant, expanding its diameter a hundredfold and swallowing the planet Mercury in the process.
The Sun will spend a few hundred million years as a red giant. Then, as nuclear reactions in its core start to sporadically fuse the helium "ash" into carbon, the Sun may begin to pulsate like the variable star Mira. Finally, as it exhausts its reserves, the Sun will throw off its outer layers to form a planetary nebula. This shell of gas will endure for a few tens of thousands of years before it dissipates into space. Eeft behind will be the white-hot core of the Sun, a white dwarf that will slowly cool and fade over billions of years.