What physical process characterizes the pre-main-sequence stage of stellar evolution?
Answer
Continued contraction increasing core temperature
Before a protostar achieves the necessary conditions for stable hydrogen fusion and officially joins the main sequence, it goes through a preparatory period known as the pre-main-sequence stage. During this time, the object is still shrinking slowly under its own gravity. This ongoing gravitational contraction is vital because it serves to further compress the core, continuously pushing the internal temperature higher and higher. Astronomers track the progress of the object through this phase by monitoring how its measurable surface temperature and luminosity change as this slow shrinkage proceeds, observing its path across the Hertzsprung-Russell diagram until fusion ignites.
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