Yellow Dwarf Stars

These medium sized stars are yellow because they have a medium temperature. Stars in this classification have a surface temperature between 5,300 and 6,000 K, and fuse hydrogen into helium to generate their light. They generally last for 10 billion years. Alpha Centauri is an example of a yellow dwarf star. Our sun is also a yellow dwarf. Near the end of their lives, these medium sized stars swell up becoming very large. When this happens to the Sun it will grow to engulf even the Earth. Eventually they shrink again, leaving behind most of their gas. This gas forms a beautiful cloud around the star called a Planetary Nebula.
When will the Sun expand into a giant, and then shrink leaving behind a planetary nebula? Don't worry; the sun is only about 5 billion years old. It still has another 5 billion years before it will expand, and then turn into a planetary nebula.
The Sun is so hot that when it dies, it will take a long time to cool off. The sun will die in about 5 billion years, but it will still glow for many billions of years after that. As it cools, it will be what is called a white dwarf star. Eventually, after billions maybe even trillions of years, it will stop glowing, at that point it will be what we call a black dwarf star. There are still no black dwarf stars in the Universe.