AST 341 Lecture Notes - Lecture 7: Globular Cluster, Rotational Energy, Energy Density
22 Dec 2016
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Document Summary
A star is de ned as an object that satis es two conditions: (a) it is bound by self-gravity (b) it radiates energy supplied by an internal source. The rst and most obvious source of energy that we could think of is gravitational energy itself. Let"s see if this is a su cient form of energy to power a star for its entire lifetime. The lifetime of the sun would then be. 4 1033 = 1015 s = 3 107 years. Since this is too short, there must be another source of energy. This other source of internal energy is provided by nuclear energy. On average, about 1 mev per particle is liberated with nuclear reactions. 1. 6 10 12) = 2 1051 erg. 4 1033 = 1. 5 109 years which is su cient to power the sun for its entire life. Nuclear (fusion) energy, indeed, constitutes the source of internal energy in stars.
