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



 
 
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  #21  
Old August 20th 06, 10:40 AM posted to sci.astro.amateur,sci.astro,alt.astronomy,alt.astronomy.solar,uk.sci.astronomy
Bluebeard
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Posts: 17
Default When the sun becomes a white dwarf why will it take SO long to cool off?



--

"Ed" wrote in message
oups.com...

So are they diamonds yet?


No, not yet

And if so, what would they radiate or
reflect being diamonds?


They would reflect, although they'd also go through a very long period of
radiating in the infra-red as the cooling process was finishing. One
imagines a flat-looking crystalline landscape in glittering white diamond,
dimly illuminated by starlight, though maybe carbon dioxide would be present
there in some form too ?

If we were to land there, in an attempt 'to walk on a star', we would be
squashed flat and resemble badly cooked omelettes.

Obviously I speak from ignorance, though in this I appear not to be alone.
Very little work seems to have been done on what these 'dead stars' would
actually be like.

Bluebeard



  #22  
Old August 20th 06, 08:55 PM posted to sci.astro.amateur,sci.astro,alt.astronomy,alt.astronomy.solar,uk.sci.astronomy
Radium
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Posts: 123
Default When the sun becomes a white dwarf why will it take SO long to cool off?


Brian Tung wrote:
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/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html


When the sun become a black dwarf, will it ever get a chance to cool to
around 70 Fahrenheit? Or will it likely form another star before?

  #23  
Old August 20th 06, 11:38 PM posted to sci.astro.amateur,sci.astro,alt.astronomy,alt.astronomy.solar,uk.sci.astronomy
Ed[_2_]
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Posts: 184
Default When the sun becomes a white dwarf why will it take SO long to cool off?


I just wondered if there is a particular wavelength that just diamonds
would re radiate?

  #24  
Old August 21st 06, 01:38 AM posted to sci.astro.amateur,sci.astro,alt.astronomy,alt.astronomy.solar,uk.sci.astronomy
Llanzlan Klazmon
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Posts: 122
Default When the sun becomes a white dwarf why will it take SO long to cool off?

"Radium" wrote in news:1156103700.335569.172140
@i3g2000cwc.googlegroups.com:


Brian Tung wrote:
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/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html


When the sun become a black dwarf, will it ever get a chance to cool to
around 70 Fahrenheit? Or will it likely form another star before?


You can do the calculation yourself. Knowing the surface area of the dwarf,
the specific heat of degenerate matter made of carbon and oxygen combined
with the Stefan-Boltzmann law. i.e radiated power goes as the fourth power
of temperature. That is good enough as a first approximation anyway. BTW,
if a black dwarf manages to accumulate additional mass through accretion
then it runs into a small problem once it reaches about 1.4 Solar masses.
At that point, the pressure caused by the object's own gravity, can no
longer be resisted by electron degeneracy pressure. This means that the
dwarf starts to collapse but now all that Carbon and Oxygen is then
available as fuel. Kablooooie. Type 1a supernova.

Klazmon.




  #25  
Old August 21st 06, 03:47 AM posted to sci.astro.amateur,sci.astro,alt.astronomy,alt.astronomy.solar,uk.sci.astronomy
Ed[_2_]
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Posts: 184
Default When the sun becomes a white dwarf why will it take SO long to cool off?


Nope Klaz, I can't....if I could I'd be on top of Mauna Kea right now

  #26  
Old August 21st 06, 05:36 AM posted to sci.astro.amateur,sci.astro,alt.astronomy,alt.astronomy.solar,uk.sci.astronomy
Radium
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Posts: 123
Default When the sun becomes a white dwarf why will it take SO long to cool off?


Llanzlan Klazmon wrote:
"Radium" wrote in news:1156103700.335569.172140
@i3g2000cwc.googlegroups.com:


Brian Tung wrote:
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/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html


When the sun become a black dwarf, will it ever get a chance to cool to
around 70 Fahrenheit? Or will it likely form another star before?


You can do the calculation yourself. Knowing the surface area of the dwarf,
the specific heat of degenerate matter made of carbon and oxygen combined
with the Stefan-Boltzmann law. i.e radiated power goes as the fourth power
of temperature. That is good enough as a first approximation anyway. BTW,
if a black dwarf manages to accumulate additional mass through accretion
then it runs into a small problem once it reaches about 1.4 Solar masses.
At that point, the pressure caused by the object's own gravity, can no
longer be resisted by electron degeneracy pressure.


This means that the
dwarf starts to collapse but now all that Carbon and Oxygen is then
available as fuel. Kablooooie. Type 1a supernova.


Correct me if I am wrong, but don't scientists beleive that the sun is
not massive enough to become a supernova?

Klazmon.




  #27  
Old August 21st 06, 05:43 AM posted to sci.astro.amateur,sci.astro,alt.astronomy,alt.astronomy.solar,uk.sci.astronomy
Brian Tung[_1_]
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Posts: 755
Default When the sun becomes a white dwarf why will it take SO long to cool off?

Radium wrote:
Correct me if I am wrong, but don't scientists beleive that the sun is
not massive enough to become a supernova?


That latter part was after the "BTW" where Klazmon qualified it by
requiring the white dwarf to have accumulated more than 1.4 solar
masses of material.

--
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
  #28  
Old August 21st 06, 05:59 AM posted to sci.astro.amateur,sci.astro,alt.astronomy,alt.astronomy.solar,uk.sci.astronomy
Llanzlan Klazmon
external usenet poster
 
Posts: 122
Default When the sun becomes a white dwarf why will it take SO long to cool off?

"Radium" wrote in
oups.com:


Llanzlan Klazmon wrote:
"Radium" wrote in news:1156103700.335569.172140
@i3g2000cwc.googlegroups.com:


Brian Tung wrote:
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/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at
http://astro.isi.edu/reference/faq.html

When the sun become a black dwarf, will it ever get a chance to cool
to around 70 Fahrenheit? Or will it likely form another star before?


You can do the calculation yourself. Knowing the surface area of the
dwarf, the specific heat of degenerate matter made of carbon and oxygen
combined with the Stefan-Boltzmann law. i.e radiated power goes as the
fourth power of temperature. That is good enough as a first
approximation anyway. BTW, if a black dwarf manages to accumulate
additional mass through accretion then it runs into a small problem
once it reaches about 1.4 Solar masses. At that point, the pressure
caused by the object's own gravity, can no longer be resisted by
electron degeneracy pressure.


This means that the
dwarf starts to collapse but now all that Carbon and Oxygen is then
available as fuel. Kablooooie. Type 1a supernova.


Correct me if I am wrong, but don't scientists beleive that the sun is
not massive enough to become a supernova?


You are correct but I specifically said the dwarf accumulated additional
matter till the point it reached 1.4 solar masses. Reread what I wrote.

Klazmon.




Klazmon.





  #29  
Old August 22nd 06, 11:22 PM posted to sci.astro.amateur,sci.astro,alt.astronomy,alt.astronomy.solar,uk.sci.astronomy
Richard Tobin
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Posts: 230
Default When the sun becomes a white dwarf why will it take SO long to cool off?

In article , Brian Tung wrote:

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.


Why does smaller surface area mean less radiation? If each particle is
radiating as much, what difference does it make how small a volume they
are contained in?

-- Richard
  #30  
Old August 22nd 06, 11:27 PM posted to sci.astro.amateur,sci.astro,alt.astronomy,alt.astronomy.solar,uk.sci.astronomy
Brian Tung[_1_]
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Posts: 755
Default When the sun becomes a white dwarf why will it take SO long to cool off?

Richard Tobin wrote:
Why does smaller surface area mean less radiation? If each particle is
radiating as much, what difference does it make how small a volume they
are contained in?


I think you're thinking of the white dwarf as an essentially transparent
object, so that you can "see" the radiation of central particles just as
easily as you can see that of the particles on the surface. If it were,
then you'd be right, and the white dwarf would cool off much faster than
it does in fact. But white dwarfs are opaque, so only the radiation
from the surface gets out unimpeded. That from particles further in
gets absorbed, keeping the white dwarf hot.

--
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
 




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