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When the sun becomes a white dwarf why will it take SO long to cool off?



 
 
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Old August 20th 06, 06:36 AM posted to sci.astro.research
Marshall Perrin
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Default When the sun becomes a white dwarf why will it take SO long to cool off?

Jonathan Thornburg -- remove -animal to reply wrote:
Ok, let's work out what determines the lifetime of a star:
To within a factor of two ot so (we're neglecting all time dependence),
the lifetime is just the ratio of the internal (thermal) energy in the
star, to the luminosity (energy radiated per unit time):


Your assumption here works fine for a white dwarf, but it's not true
in the case of the sun. Remember that little thing called nuclear
fusion? The fusing of nuclei in the core of the sun provides an energy
reservoir many orders of magnitude larger than the sun's internal
thermal energy. The sun's lifetime would be tremendously shorter than
it really is, were it only to be cooling with no internal source of
more energy.

- Marshall
 




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