I learned recently that pre-main sequence stars (those fueled by their own gravitational collapse) are typically much brighter, by up to an order of magnitude, than their successor main sequence stars:
The reason for this is that the young star has comparable surface temperature to a mature star while being physically much larger, so gives off more light. In fact, for fully convective stars the surface temperature is almost solely a function of the mass of the star and largely independent of its radius:
Unrelated:
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