If all stars suddenly stopped producing heat (or heating up) which stars would cool to absolute zero first and how long would it take?
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$\begingroup$ some details about the effect you were interested in this article $\endgroup$– symbiotechCommented May 13, 2014 at 20:37
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1 Answer
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In our current universe white dwarfs are the first ones that should cool, because they are already "cold" (not producing anything anymore, just radiating heat) remnants of a former star. The time for this to happen is disputed (10^15 or 10^37 years), but is far bigger than the age of universe, so nobody expects to find one "cooled star" yet. See this article for details on "black dwarfs" as they are called.
In your sudden stop hypothetical universe probably the first one to cool would be the smallest and coolest stars, a M9V red dwarf (with 7.5% solar mass, 8% solar radius, 2,300K temperature). Note that brown dwarfs are categorized as substellar objects, so they shouldn't be considered. I don't think the poorly understood "Mpemba effect" can be yet applied to stars.
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$\begingroup$ But then why are white dwarves the hottest of the four groups of stars $\endgroup$– user1553Commented May 4, 2014 at 14:24
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$\begingroup$ As pointed out, this is incorrect as white dwarfs are the hottest (they wouldn't be white if they weren't). Are you thinking of brown dwarfs? $\endgroup$ Commented May 4, 2014 at 14:26
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$\begingroup$ But with white dwarfs being the hottest, surely the Mpemba effect would come in to effect $\endgroup$ Commented May 4, 2014 at 14:27
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3$\begingroup$ The consideration of brown dwarfs as a star is disputed, but generally they are considered substellar objects, and thus wouldn't fit the terms of your question. Presumably, the answerer refers to white dwarfs as cold to indicate that they have ceased core reactions and compression, and have begun the long process of cooling. These would likely cool first, even if all other stars suddenly stopped producing heat (as per your question), as they have a head start. $\endgroup$ Commented May 4, 2014 at 14:32
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3$\begingroup$ The Mpemba effect is not well defined and the parameters to observe it are not generally clear. Regardless this affect is generally discussed regarding water with (relative to astronomical bodies) very small temperature differences in far more complex environments. Given that, it would be hard to extrapolate the Mpemba effect to this level. Personally, I doubt it. $\endgroup$ Commented May 4, 2014 at 14:47