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Main
Date: 18 Aug 2006 12:56:14
From: Radium
Subject: When the sun becomes a white dwarf why will it take SO long to cool off?
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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
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Date: 18 Aug 2006 23:22:47
From: RT
Subject: Re: When the sun becomes a white dwarf why will it take SO long to cool
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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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Date: 18 Aug 2006 22:34:33
From: Sam Wormley
Subject: Re: When the sun becomes a white dwarf why will it take SO long to
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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.
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Date: 19 Aug 2006 01:44:45
From: jacob navia
Subject: Re: When the sun becomes a white dwarf why will it take SO long to
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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.
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Date: 19 Aug 2006 00:25:52
From: Sam Wormley
Subject: Re: When the sun becomes a white dwarf why will it take SO long to
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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.
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Date: 19 Aug 2006 11:53:53
From: Boo
Subject: Re: When the sun becomes a white dwarf why will it take SO long to
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> Besides being degenerate, white dwarf are mostly carbon
> and oxygen.
Ideal places to saearch for extra-terrestrial life in fact ?
--
Boo
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Date: 19 Aug 2006 13:05:08
From: Sam Wormley
Subject: Re: When the sun becomes a white dwarf why will it take SO long to
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Boo wrote:
>> Besides being degenerate, white dwarf are mostly carbon
>> and oxygen.
>
> Ideal places to saearch for extra-terrestrial life in fact ?
>
Degenerate matter life? Could be a problem.
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Date: 19 Aug 2006 17:40:25
From: Boo
Subject: Re: When the sun becomes a white dwarf why will it take SO long to
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Sam Wormley wrote:
> Boo wrote:
>>> Besides being degenerate, white dwarf are mostly carbon
>>> and oxygen.
>>
>> Ideal places to saearch for extra-terrestrial life in fact ?
>
> Degenerate matter life? Could be a problem.
So chemistry doesn't work, who needs it anyway ?
--
Boo
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Date: 30 Aug 2006 14:33:26
From: Joseph Lazio
Subject: Re: When the sun becomes a white dwarf why will it take SO long to cool off?
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>>>>> "SW" == Sam Wormley <swormley1@mchsi.com> writes:
SW > 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.
SW > Besides being degenerate, white dwarf are mostly carbon and
SW > oxygen.
I think that's only true of some WDs. The composition of a WD depends
upon what its progenitor mass was. Stars less massive than the Sun I
believe are expected to become helium WDs because they don't have the
mass to initiate the fusion of He to C.
--
Lt. Lazio, HTML police
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Date: 31 Aug 2006 16:58:44
From: Steve Willner
Subject: Re: When the sun becomes a white dwarf why will it take SO long to cool off?
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SW > ...white dwarf are mostly carbon and oxygen.
In article <ypz4pvuxedl.fsf@adams.patriot.net >,
Joseph Lazio <jlazio@adams.patriot.net > writes:
> I think that's only true of some WDs. The composition of a WD depends
> upon what its progenitor mass was. Stars less massive than the Sun I
> believe are expected to become helium WDs because they don't have the
> mass to initiate the fusion of He to C.
Joe is correct, of course. I don't know what the dividing line is;
those courses were a long time ago! I vaguely recall it's quite a
bit less than a solar mass but could easily be wrong. I don't
suppose it's too much lower than a solar mass, though, or no helium
white dwarfs would yet have formed. White dwarfs with helium and
even hydrogen _atmospheres_ exist, but that doesn't necessarily
reflect the interior composition.
--
Steve Willner Phone 617-495-7123 swillner@cfa.harvard.edu
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
email may be sent to your ISP.)
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Date: 19 Aug 2006 00:22:08
From: Sam Wormley
Subject: Re: When the sun becomes a white dwarf why will it take SO long to
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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".
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Date: 18 Aug 2006 16:54:09
From: Brian Tung
Subject: Re: When the sun becomes a white dwarf why will it take SO long to
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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 <brian@isi.edu >
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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Date: 18 Aug 2006 13:03:43
From: Brian Tung
Subject: Re: When the sun becomes a white dwarf why will it take SO long to cool off?
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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 <brian@isi.edu >
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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Date: 22 Aug 2006 22:22:02
From: Richard Tobin
Subject: Re: When the sun becomes a white dwarf why will it take SO long to cool off?
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In article <ec56ev$3k9$1@praesepe.isi.edu >, Brian Tung <brian@isi.edu> 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
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Date: 22 Aug 2006 15:27:56
From: Brian Tung
Subject: Re: When the sun becomes a white dwarf why will it take SO long to cool off?
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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 <brian@isi.edu >
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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Date: 29 Aug 2006 13:41:04
From: Llanzlan Klazmon
Subject: Re: When the sun becomes a white dwarf why will it take SO long to cool off?
|
richard@cogsci.ed.ac.uk (Richard Tobin) wrote in
news:ecg02a$1eu3$1@pc-news.cogsci.ed.ac.uk:
> In article <ec56ev$3k9$1@praesepe.isi.edu>, Brian Tung <brian@isi.edu>
> 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?
The radiation is only from the surface as the bulk of the white dwarf is
essentially opaque. It is an interesting point though with respect to
neutron stars. When they are initially formed, their temperature is
expected be of the order of 10^11 K degrees. However their initial rate of
cooling is much faster than you would expect from the Stefan-Boltzmann law
applied to their surface area. The reason is that much of their initial
heat energy is lost via neutrino emission rather than photons. A large
percentage of the neutrinos can escape from the bulk of the neutron star
unimpeded as the neutron star is largely transparent to neutrinos.
http://arxiv.org/PS_cache/astro-ph/pdf/0409/0409751.pdf
Klazmon
>
> -- Richard
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Date: 18 Aug 2006 13:06:31
From: Double-A
Subject: Re: 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
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Date: 18 Aug 2006 20:05:32
From: Sco
Subject: Re: 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" <glucegen1@excite.com > wrote in message
news:1155930974.846458.107150@m73g2000cwd.googlegroups.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
>
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Date: 19 Aug 2006 01:13:37
From: John Carruthers
Subject: Re: 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 <brian@isi.edu>
> 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
An exemplary answer Mr. Tung ;-) I only wish I'd written that in my
last exam ;-(
jc
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Date: 19 Aug 2006 22:18:58
From: Bluebeard
Subject: Re: When the sun becomes a white dwarf why will it take SO long to cool off?
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"Radium" <glucegen1@excite.com > wrote in message
news:1155930974.846458.107150@m73g2000cwd.googlegroups.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
>
This is what was dealt with in response to my question to 'Ask Alan' in the
September 'Astronomy Now'. Although he did re-phrase my question somewhat,
in the main it was answered. Despite many previous tries, it's the first
time anybody actually has...
These dead stars, black dwarves, 'cinders', call them what-you-will, have
always fascinated me because their actual nature is always glossed over in
astronomy texts.
We learn from Alan:
1) These earth-sized objects have probably become spherical diamonds by the
time they cool.
2) Cooling to ambient takes of the order of 25 billion years - so none exist
yet.
3) The tallest possible mountains on these dead stars are about 200 metres
high. I was surprised by this - I rather expected a ball-bearing smooth
body, but then diamonds are pretty hard and resist compression well, eh ?
Bluebeard
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Date: 19 Aug 2006 13:39:55
From: Radium
Subject: Re: When the sun becomes a white dwarf why will it take SO long to cool off?
|
Sam Wormley wrote:
> 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.
At the high-temperatures white dwarfs are, won't the carbon and oxygen
combine to form CO2?
AFAIK, complete oxidation of carbon yields carbon dioxide.
The temperatures of white dwarfs are FAR more than enough to burn the
carbon with oxygen and form CO2.
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Date: 19 Aug 2006 23:41:16
From: Sam Wormley
Subject: Re: When the sun becomes a white dwarf why will it take SO long to
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Radium wrote:
> Sam Wormley wrote:
>> 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.
>
> At the high-temperatures white dwarfs are, won't the carbon and oxygen
> combine to form CO2?
>
> AFAIK, complete oxidation of carbon yields carbon dioxide.
>
> The temperatures of white dwarfs are FAR more than enough to burn the
> carbon with oxygen and form CO2.
>
White Dwarf
http://scienceworld.wolfram.com/physics/WhiteDwarf.html
http://imagine.gsfc.nasa.gov/docs/science/know_l2/dwarfs.html
"With a surface gravity of 100,000 times that of the earth, the
atmosphere of a white dwarf is very strange. The heavier atoms in
its atmosphere sink and the lighter ones remain at the surface.
Some white dwarfs have almost pure hydrogen or helium atmospheres,
the lightest of elements. Also, the very strong gravity pulls the
atmosphere close around it in a very thin layer, that, if were it
on earth, would be lower than the tops of our skyscrapers!
"Underneath the atmosphere of many white dwarfs, scientists think
there is a 50 km thick crust, the bottom of which is a crystalline
lattice of carbon and oxygen atoms. One might make the comparison
between a cool carbon/oxygen white dwarf and a diamond! (After all,
a diamond is just crystallized carbon!)"
Electron Degeneracy Pressure
http://scienceworld.wolfram.com/physics/ElectronDegeneracyPressure.html
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Date: 19 Aug 2006 13:37:33
From: Radium
Subject: Re: When the sun becomes a white dwarf why will it take SO long to cool off?
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Ed wrote:
> So there are not any stone cold dead white dwarfs?
If they are cold [as cold as the surrounding outer space], then they
are "black" dwarfs
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Date: 19 Aug 2006 10:28:10
From: Ed
Subject: Re: When the sun becomes a white dwarf why will it take SO long to cool off?
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So there are not any stone cold dead white dwarfs?
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Date: 19 Aug 2006 20:45:05
From: Ed
Subject: Re: When the sun becomes a white dwarf why will it take SO long to cool off?
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So are they diamonds yet?
And if so, what would they radiate or
reflect being diamonds?
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Date: 20 Aug 2006 10:40:11
From: Bluebeard
Subject: Re: When the sun becomes a white dwarf why will it take SO long to cool off?
|
--
"Ed" <ed1ward2@verizon.net > wrote in message
news:1156045505.893459.181450@p79g2000cwp.googlegroups.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
>
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Date: 20 Aug 2006 21:36:43
From: Radium
Subject: Re: When the sun becomes a white dwarf why will it take SO long to cool off?
|
Llanzlan Klazmon wrote:
> "Radium" <glucegen1@excite.com> 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 <brian@isi.edu>
> >> 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.
>
>
> >
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Date: 20 Aug 2006 21:43:28
From: Brian Tung
Subject: Re: 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 <brian@isi.edu >
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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Date: 21 Aug 2006 16:59:55
From: Llanzlan Klazmon
Subject: Re: When the sun becomes a white dwarf why will it take SO long to cool off?
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"Radium" <glucegen1@excite.com > wrote in
news:1156135003.662838.100320@m73g2000cwd.googlegroups.com:
>
> Llanzlan Klazmon wrote:
>> "Radium" <glucegen1@excite.com> 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 <brian@isi.edu>
>> >> 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.
>>
>>
>> >
>
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Date: 20 Aug 2006 19:47:34
From: Ed
Subject: Re: When the sun becomes a white dwarf why will it take SO long to cool off?
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Nope Klaz, I can't....if I could I'd be on top of Mauna Kea right now:)
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Date: 20 Aug 2006 15:38:46
From: Ed
Subject: Re: When the sun becomes a white dwarf why will it take SO long to cool off?
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I just wondered if there is a particular wavelength that just diamonds
would re radiate?
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Date: 20 Aug 2006 12:55:00
From: Radium
Subject: Re: When the sun becomes a white dwarf why will it take SO long to cool off?
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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 <brian@isi.edu>
> 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?
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Date: 21 Aug 2006 12:38:14
From: Llanzlan Klazmon
Subject: Re: When the sun becomes a white dwarf why will it take SO long to cool off?
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"Radium" <glucegen1@excite.com > 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 <brian@isi.edu>
>> 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.
>
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