It might seem strange to think that something so big could ever die, but stars have a life span, just as people do. True, we're talking about extremely long lives -- on the order of billions of years -- but stars have a beginning, middle and end of life just the same. And their "funerals" are staggeringly elaborate. Red giants and white dwarfs are simply different stages in the life of a star. After a star has burned up all its fuel, it can expand into a red giant, growing ever larger and casting off its outer shell. Then the center of the star contracts to form a small but extremely dense and intensely hot white dwarf. This will happen to our own sun in another 5 billion years or so.
The whole question of a star's life span hinges on the star's mass. A star that's approximately the size of our sun (which, incidentally, is only a very ordinary star -- nothing special, astronomically speaking, despite the 6 billion people to whom it gives life) takes roughly 50 million years to reach maturity. That period is called the main sequence. It will remain in that phase for about 10 billion years. The center of our solar system is also known as a "g"-type star. The "g" refers to the sun's color and temperature. Put those two descriptions together and you'll have the classification for our sun: a g-type main sequence star.
As we said, though, size -- or, mass -- matters where stars are concerned. Stars that are larger and brighter than our sun burn out much faster. They're not too big to fail. In fact, it's more accurate to say they're so big they must fail. They simply burn their fuel too inefficiently. For example, Wolf-Rayet stars, which may have masses 20 times that of the sun and get 4.5 times as hot, can go supernova (bursting in a giant explosion, something not all stars do) within a few million years of hitting main sequence.
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