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Is stellar ignition an instantaneous thing - before, dark, after, shining brightly - or more of a process over time? In fusion research 'ignition' appears to be an event, but maybe in a protostar it starts locally and then spreads?

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    $\begingroup$ This is not a meaningful question - any process in physics, a.k.a. the universe, has a timescale asociated with it. The process in question always happens on this timescale. The only thing we can meaningfully do, is compare different timescales, i.e. if one is much shorter than the other. $\endgroup$ – AtmosphericPrisonEscape May 12 '19 at 9:54
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    $\begingroup$ This is an interesting question but the answer is complex, and our knowledge of it is far from certain. There is a good discussion on the older question Timescale of ignition of a protostar? which is why I and others are voting to close this as a duplicate. If you feel the answers to that other question do not answer your question, feel free to ask a new question which tries to emphasise the difference with that one. $\endgroup$ – Steve Linton May 12 '19 at 12:17
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    $\begingroup$ Actually, it's not the same question, because this question is about how the star "turns on" like a light, and exhibits confusion between that and the onset of fusion-- which is completely different. Fusion onset does not change the luminosity of a star, it merely allows the star to achieve equilibrium and a more gradual evolution rate. So this should be emphasized in the answer to this question-- regardless of the timescale for fusion to begin, the star is already bright. $\endgroup$ – Ken G May 12 '19 at 18:25
  • $\begingroup$ @KenG fyi I've just asked the above question in meta. $\endgroup$ – uhoh Apr 3 at 3:29

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