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When the sun becomes a white dwarf why will it take SO long to cool off?
In article , Radium wrote:
I've read about the sun's life cycle. Apparently, when the sun becomes a white dwarf, it will take at least a trillion years to completely cool off. Why such a long time? It's heavy and it's hot, but it's only got a small surface area to radiate it's heat through. So, to allow the heat out through that small area is going to take a long time. It seems that the sun would exist much longer dead [i.e. as a white dwarf] than alive [burning hydrogen and helium]. White dwarfs aren't dead. They're not producing any new energy (by conversion of mass through fusion), but they've got a *lot* of stored energy in both thermal and heat forms ; they've got quite considerable rotational energy; and many of them have significant magnetic fields too. All these are signs of something non-dead. When a white dwarf has radiated it's thermal energy to the point that it's internal convection is too slow to maintain a magnetic field and it's just a dark (well, IR-radiating) body with considerable mass and rotation, then it's a black dwarf. And it's lifetime as that is in the order of 10^20 times as long as the present age of the universe. Assuming that protons are long-term unstable. Which is not accepted, let alone proven. -- Aidan Karley, FGS Aberdeen, Scotland Written at Sat, 19 Aug 2006 16:43 +0100, but posted later. |
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