１３−１ The Birth of Stars
In the universe,
Stars are born from chaos.
Stars and intelligence are being born while increasing the entropy.
※ entropy: the degree of disorder
※ law of entropy increase: the laws of increasing of disorder in the universe
１３−２ Life of Stars
○Big star burns out faster than small one.
（Since stars have a limited supply of hydrogen in their cores, they have a limited lifetime as main sequence stars. This lifetime is proportional to f M / L, where f is the fraction of the total mass of the star, M, available for nuclear burning in the core and L is the average luminosity of the star during its main sequence lifetime. Because of the strong dependence of luminosity on mass, stellar lifetimes depend sensitively on mass.）
○The lifetime of the sun is about 100 million years. The life of stars of 10 times weight of the sun is from 1 / 1000 to 1 / 100.
○The Sun formed about 4.6 billion years ago. It will exit the main sequence in approximately 5 billion years and start to turn into a red giant.