What critical temperature threshold must the protostar core exceed for nuclear fusion to commence?
Answer
Approximately 15 million degrees Celsius
The transition from a collapsing protostar to a true, stable star hinges on reaching an extraordinary core temperature. When the density and internal energy become high enough, the hydrogen nuclei within the core achieve sufficient kinetic energy to overcome their natural electrostatic repulsion, which normally forces them apart. This threshold is precisely stated as about 15 million degrees Celsius (or 27 million degrees Fahrenheit). At this point, the nuclei collide with enough force to fuse together, forming helium nuclei and releasing thermonuclear energy, which provides the necessary outward pressure to halt gravitational collapse.
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