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



 
 
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  #1  
Old August 18th 06, 08:56 PM posted to sci.astro.amateur,sci.astro,alt.astronomy,alt.astronomy.solar,uk.sci.astronomy
Radium
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Default When the sun becomes a white dwarf why will it take SO long to cool off?

Hi:

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 seems that the sun would exist much longer dead [i.e. as a white
dwarf] than alive [burning hydrogen and helium].

Any assistance on this matter is appreciated.


Thanks,

Radium

  #2  
Old August 18th 06, 09:03 PM posted to sci.astro.amateur,sci.astro,alt.astronomy,alt.astronomy.solar,uk.sci.astronomy
Brian Tung[_1_]
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Default When the sun becomes a white dwarf why will it take SO long to cool off?

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?


Because at that point, the Sun will still have a lot of heat left, but
it will be radiating it much slower than it does now.

A white dwarf is the hot exposed core of the progenitor star. As such,
it contains most of the heat that was in the star at the time that it
died. But the white dwarf radiates heat much slower than it did when
the star was alive, simply because its surface area is so much smaller.

The Sun as a white dwarf will be, let's say, 100 times smaller (by
diameter) than it is now, meaning it will be 10,000 times smaller by
area. To be sure, it will initially be quite hot, perhaps four times
hotter (in kelvins) than it is now, so it'll radiate tens of times more
energy per unit area than it does now. Still, that means that its
overall rate of radiation (and therefore rate of cooling) will be
several hundreds of times slower than it is now.

That factor will only increase as the Sun cools down, and the rate at
which it radiates off into space slows down. It will approach the cold
of interstellar space only very slowly at the end.

--
Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
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  #3  
Old August 18th 06, 09:05 PM posted to sci.astro.amateur,sci.astro,alt.astronomy,alt.astronomy.solar,uk.sci.astronomy
Sco
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Default When the sun becomes a white dwarf why will it take SO long to cool off?

In my research, The temperature of earth core is 2000 C warmer than the Sun.
The Earth took a long time to cool off.


"Radium" wrote in message
oups.com...
Hi:

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 seems that the sun would exist much longer dead [i.e. as a white
dwarf] than alive [burning hydrogen and helium].

Any assistance on this matter is appreciated.


Thanks,

Radium



  #4  
Old August 18th 06, 09:06 PM posted to sci.astro.amateur,sci.astro,alt.astronomy,alt.astronomy.solar,uk.sci.astronomy
Double-A[_1_]
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Default When the sun becomes a white dwarf why will it take SO long to cool off?


Radium wrote:
Hi:

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?



That does seem strange, since neutron stars cool relatively quickly due
to neutrino emmission. Of course neutron stars get a lot hotter than
white dwarf stars.


It seems that the sun would exist much longer dead [i.e. as a white
dwarf] than alive [burning hydrogen and helium].



So will you.

Double-A


Any assistance on this matter is appreciated.


Thanks,

Radium


  #5  
Old August 18th 06, 11:34 PM posted to sci.astro.amateur,sci.astro,alt.astronomy,alt.astronomy.solar,uk.sci.astronomy
Sam Wormley
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Default When the sun becomes a white dwarf why will it take SO long tocool off?

Radium wrote:
Hi:

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?


Small surface area.



It seems that the sun would exist much longer dead [i.e. as a white
dwarf] than alive [burning hydrogen and helium].


It will exist far longer as a cold degenerate body.

  #6  
Old August 19th 06, 12:44 AM posted to sci.astro.amateur,sci.astro,alt.astronomy,alt.astronomy.solar,uk.sci.astronomy
jacob navia
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Default When the sun becomes a white dwarf why will it take SO long tocool off?

Sam Wormley wrote:
Radium wrote:

Hi:

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?



Small surface area.



It seems that the sun would exist much longer dead [i.e. as a white
dwarf] than alive [burning hydrogen and helium].



It will exist far longer as a cold degenerate body.


Excuse me but what is "degenerate" in a white dwarf?

I mean they are made of normal matter, albeit very
concentrated, not neutron stars, nor quark stars, just
balls of iron and heavy elements at very high densities.

Nothing degenerate at all.
  #7  
Old August 19th 06, 12:54 AM posted to sci.astro.amateur,sci.astro,alt.astronomy,alt.astronomy.solar,uk.sci.astronomy
Brian Tung[_1_]
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Default When the sun becomes a white dwarf why will it take SO long tocool off?

jacob navia wrote:
Excuse me but what is "degenerate" in a white dwarf?

I mean they are made of normal matter, albeit very
concentrated, not neutron stars, nor quark stars, just
balls of iron and heavy elements at very high densities.

Nothing degenerate at all.


White dwarfs are held up by electron degeneracy--the Pauli exclusion
principle as applied to the electrons in the white dwarf. It keeps the
matter from getting squeezed in further. That is probably what Sam
meant.

Incidentally, white dwarfs do not typically contain iron; stars small
enough to form white dwarfs (as opposed to neutron stars or black holes)
aren't massive enough to fuse that far.

--
Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
  #8  
Old August 19th 06, 01:22 AM posted to sci.astro.amateur,sci.astro,alt.astronomy,alt.astronomy.solar,uk.sci.astronomy
Sam Wormley
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Default When the sun becomes a white dwarf why will it take SO long tocool off?

jacob navia wrote:
Sam Wormley wrote:
Radium wrote:

Hi:

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?



Small surface area.



It seems that the sun would exist much longer dead [i.e. as a white
dwarf] than alive [burning hydrogen and helium].



It will exist far longer as a cold degenerate body.


Excuse me but what is "degenerate" in a white dwarf?

I mean they are made of normal matter, albeit very
concentrated, not neutron stars, nor quark stars, just
balls of iron and heavy elements at very high densities.

Nothing degenerate at all.


Background
http://en.wikipedia.org/wiki/Degenerate_matter

"Unlike a classical ideal gas, whose pressure is proportional to its
temperature (PV = nkT, where P is pressure, V is the volume, n is
the number of particles (typically atoms or molecules), k is
Boltzmann's constant, and T is temperature), the pressure exerted
by degenerate matter depends only weakly on its temperature. In
particular, the pressure remains nonzero even at absolute zero
temperature. At relatively low densities, the pressure of a fully
degenerate gas is given by P = Kn^5/3, where K depends on the
properties of the particles making up the gas. At very high
densities, where most of the particles are forced into quantum
states with relativistic energies, the pressure is given by P =
K'n^4/3, where K' again depends on the properties of the particles
making up the gas".

  #9  
Old August 19th 06, 01:25 AM posted to sci.astro.amateur,sci.astro,alt.astronomy,alt.astronomy.solar,uk.sci.astronomy
Sam Wormley
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Posts: 836
Default When the sun becomes a white dwarf why will it take SO long tocool off?

jacob navia wrote:

Excuse me but what is "degenerate" in a white dwarf?

I mean they are made of normal matter, albeit very
concentrated, not neutron stars, nor quark stars, just
balls of iron and heavy elements at very high densities.

Nothing degenerate at all.


Besides being degenerate, white dwarf are mostly carbon
and oxygen.
  #10  
Old August 19th 06, 05:22 AM posted to sci.astro.amateur,sci.astro,alt.astronomy,alt.astronomy.solar,uk.sci.astronomy
RT[_1_]
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Default When the sun becomes a white dwarf why will it take SO long to cooloff?



Radium wrote:

Hi:

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?


Because as a condensed mass it will be far more efficient at conserving
its energy
and mass compared to how it radiated during the hyrdogen phase.



It seems that the sun would exist much longer dead [i.e. as a white
dwarf] than alive [burning hydrogen and helium].


Not exactly dead by any means, just different but still very much alive
compared
to how you will be molding in the grave!


Any assistance on this matter is appreciated.

Thanks,

Radium


 




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