The life of a star depends only on how much mass the star has. Stars that are 10 times the mass of the Sun will last about 100 million years. Stars with about the Sun's mass last about 13 billion years, and stars about one tenth the mass of our Sun last 100 billion years or longer.
These are rough estimates, but they can be made very precise by astronomers who study the physics of how stars evolve and change with time. As for what the average life time of a star is, it turns out that the average star in our Milky Way is a bit less massive that our Sun. If we look at all the stars near the Sun, we see that most of them are so dim that we would not be able to directly see them in the rest of the Milky Way. They are far more numerous than the dazzling, bright stars we see in the sky with our naked eyes. The average star has a mass of about half that of our Sun, so that means that the average star in our galaxy will live about 50 billion years or so.
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