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    | • | As star converts H to He you 
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    |  | have more massive nuclei 
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    |  | – | Pressure related to number of nuclei 
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    |  | 
   
    |  | – | Gravity related to mass of nuclei 
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    |  | • | Pressure would tend to drop unless 
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    |  | something else happens 
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    | • | Temperature must rise (slightly) 
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    |  | to compensate 
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    | • | Luminosity  must  rise (slightly) 
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    |  | as heat leaks out faster 
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