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I was recently watching a video about the life of the universe at its end... and then tried to correlate that to what I could find in recognized papers that I could download. (as I am not a scientist or student, a lot of the papers they have access to, I do not not, so I am kind of limited.)

One article by Nature Magazine, stated that for a stellar mass black hole, somewhere around 10^71 seconds, the Hawking radiation output in the last .1 seconds would be around 10^30 ergs. (A small explosion on a cosmic level to be sure)...

But my question is before this.... As the black hole shrinks is it always just at the point where for its size, it is a black hole? Is there ever a point, where the BH expands again?

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There is no point at which it expands. The radius of a black hole is proportional to its mass. As the hole radiates energy to infinity, it loses energy and thus mass, so its radius shrinks. It remains a black hole.

You can find some (crude) formulas and calculations in this other answer.

At some point the hole becomes so small that we don’t understand what happens because describing it would require a theory of quantum gravity and we don’t yet have one that is widely accepted. So perhaps something weird happens at the very end when its radius is on the order of the Planck length.

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  • $\begingroup$ Thank you very much G. Smith. It is, as I thought... One follow up question... As the last of the BH evaporates away, at what point does the event horizon become as small as the BH itself? I would assume this is at the moment when the last energy radiates away, but could it be sooner? $\endgroup$ – Rick Feb 26 '20 at 20:58
  • $\begingroup$ At what point does the event horizon become as small as the BH itself? Physicists consider the event horizon to determine the size of the hole. What else would? It’s not like there is anything inside, like a dense shrunken star. There is just a singularity. The “hole” means “the interior of the horizon”. $\endgroup$ – G. Smith Feb 26 '20 at 21:02

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