What is the dominant energy source for a protostar before nuclear fusion begins?
Answer
Gravitational contraction
A protostar is defined by its energy generation mechanism, which predates the onset of sustained nuclear reactions in its core. During the protostar phase, the object is luminous and hot because the immense gravitational potential energy inherent in the collapsing mass is continuously converted into kinetic energy as material falls inward. This kinetic energy then transforms into thermal energy (heat) through particle collisions during contraction. This squeezing action generates the significant heat observed, allowing the object to glow brightly for millions of years without actually fusing hydrogen atoms, which requires a much higher core temperature.
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