What change slowly occurs during the main-sequence lifetime of a star?
A) As hydrogen is used up in the core, the fusion rate decreases and reduces the luminosity.
B) It gathers more gas from interstellar space, increasing its mass and hence the luminosity.
C) Its core temperature slowly increases, increasing the fusion rate and hence the luminosity.
D) As the solar wind blows material into space, the decreasing mass reduces pressure in the core, which in turn reduces the fusion rate and the luminosity.
C
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