Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Stellar evolution is the process by which a star undergoes a sequence of radical changes during its lifetime. Depending on the mass of the star, this lifetime ranges from only a few million years for the most massive to trillions of years for the least massive, which is considerably longer than the age of the universe. Learn more about stars, their birth, life and spectacular death in fiery supernovas in the following pages.