Approximately what core temperature must be reached for hydrogen fusion to ignite in a protostar?
Answer
15 million Kelvin
The transition from a contracting protostar to a stable main-sequence star is marked by the precise moment nuclear fusion ignites within the core. This ignition requires the core material to achieve a critical threshold of both density and temperature, overcoming the electrostatic repulsion between the positively charged hydrogen nuclei. Specifically, the text notes that when the core temperature reaches approximately 15 million Kelvin, the conditions become sufficient for the hydrogen fusion process to begin. Once this fusion initiates and generates enough outward pressure to counteract the inward gravitational force, the star achieves hydrostatic balance and officially joins the main sequence.
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