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Main
Date: 13 Jul 2007 19:45:36
From: Radium
Subject: How long will the sun remain a white dwarf?
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Hi:
When the sun becomes a white dwarf, approximately how long will it
take for it to cool off to a cold black dwarf that does not emit
anymore heat or light [or other energies] than the surrounding space?
Thanks,
Radium
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Date: 18 Jul 2007 13:59:15
From:
Subject: Re: How long will the sun remain a white dwarf?
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On Fri, 13 Jul 2007 19:45:36 -0000, Radium <glucegen1@gmail.com >
wrote:
>Hi:
>
>When the sun becomes a white dwarf, approximately how long will it
>take for it to cool off to a cold black dwarf that does not emit
>anymore heat or light [or other energies] than the surrounding space?
>
>
>Thanks,
>
>Radium
Hasn't the recent discovery that the Universe's expanse is
accelerating put an upper limit on the lifetime of the Unverse? Or at
least the lifetime before every particle is froced apart from al te
particles? Of course I'm sure that with in another 20 years someone
will make another discovery which will throw that model out as well.
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Date: 18 Jul 2007 14:22:07
From: Chris L Peterson
Subject: Re: How long will the sun remain a white dwarf?
|
On Wed, 18 Jul 2007 13:59:15 GMT, Passing through
Pass_Through@yahoo.com wrote:
>Hasn't the recent discovery that the Universe's expanse is
>accelerating put an upper limit on the lifetime of the Unverse?
Just the opposite. If the observation is correct, it means the Universe
will continue to expand forever.
>Or at
>least the lifetime before every particle is froced apart from al te
>particles?
That won't happen. Gravity will still hold things together locally. All
that will happen is that everything will drift towards absolute zero
(but never quite get there). If baryon decay turns out to be real, the
Universe might ultimately consist of nothing but exotic subatomic
particles, but that question remains open.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 21 Jul 2007 05:45:00
From:
Subject: Re: How long will the sun remain a white dwarf?
|
On Wed, 18 Jul 2007 14:22:07 GMT, Chris L Peterson
<clp@alumni.caltech.edu > wrote:
>On Wed, 18 Jul 2007 13:59:15 GMT, Passing through
>Pass_Through@yahoo.com wrote:
>
>>Hasn't the recent discovery that the Universe's expanse is
>>accelerating put an upper limit on the lifetime of the Unverse?
>
>Just the opposite. If the observation is correct, it means the Universe
>will continue to expand forever.
>
>>Or at
>>least the lifetime before every particle is froced apart from al te
>>particles?
>
>That won't happen. Gravity will still hold things together locally. All
>that will happen is that everything will drift towards absolute zero
>(but never quite get there). If baryon decay turns out to be real, the
>Universe might ultimately consist of nothing but exotic subatomic
>particles, but that question remains open.
>
>_________________________________________________
>
>Chris L Peterson
>Cloudbait Observatory
>http://www.cloudbait.com
Haven't you heard of the Big Rip Theory? It seems that several
Cosmologists feel that this may be the fate of the Universe. One link
is below.
http://www.space.com/scienceastronomy/big_rip_030306.html
If this theory is true then it does put an upper limit on how long the
Sun will remain in the white dwarf stage. I suspect that if this
theory is true the Sun will have cooled so it no longer appears white.
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Date: 21 Jul 2007 13:47:34
From: Chris L Peterson
Subject: Re: How long will the sun remain a white dwarf?
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On Sat, 21 Jul 2007 05:45:00 GMT, Passing_Through@nowhere.org wrote:
>Haven't you heard of the Big Rip Theory? It seems that several
>Cosmologists feel that this may be the fate of the Universe. One link
>is below.
That's extremely speculative at the moment. Mainstream thought has the
Universe simply cooling forever.
>If this theory is true then it does put an upper limit on how long the
>Sun will remain in the white dwarf stage. I suspect that if this
>theory is true the Sun will have cooled so it no longer appears white.
Depends on what you mean by white. In 20 billion or so years, the Sun
will still be very hot and certainly glowing brightly.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 21 Jul 2007 16:06:51
From:
Subject: Re: How long will the sun remain a white dwarf?
|
On Sat, 21 Jul 2007 13:47:34 GMT, Chris L Peterson
<clp@alumni.caltech.edu > wrote:
>On Sat, 21 Jul 2007 05:45:00 GMT, Passing_Through@nowhere.org wrote:
>
>>Haven't you heard of the Big Rip Theory? It seems that several
>>Cosmologists feel that this may be the fate of the Universe. One link
>>is below.
>
>That's extremely speculative at the moment. Mainstream thought has the
>Universe simply cooling forever.
>
>
>>If this theory is true then it does put an upper limit on how long the
>>Sun will remain in the white dwarf stage. I suspect that if this
>>theory is true the Sun will have cooled so it no longer appears white.
>
>Depends on what you mean by white. In 20 billion or so years, the Sun
>will still be very hot and certainly glowing brightly.
>
>_________________________________________________
>
>Chris L Peterson
>Cloudbait Observatory
>http://www.cloudbait.com
It seems a logica consequence IF the expansion is accelrating. At
somepoint it should overcome even gravity. Of course who is to say
the accelration will continue forever. I am certain someone will come
up with a new theory in other decade or so.
By white i was referring to the color. I am sure it will still be
bright, but I am thinking it may well be yellowish after 20 billion
years.
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Date: 20 Jul 2007 19:45:23
From: George Dishman
Subject: Re: How long will the sun remain a white dwarf?
|
"Chris L Peterson" <clp@alumni.caltech.edu > wrote in message
news:v28s931mk0mmm6m9ad33uekr2j0q1hmv7o@4ax.com...
> On Wed, 18 Jul 2007 13:59:15 GMT, Passing through
> Pass_Through@yahoo.com wrote:
>
...
>
>>Or at
>>least the lifetime before every particle is froced apart from al te
>>particles?
>
> That won't happen. Gravity will still hold things together locally.
I think he is thinking of ..
http://en.wikipedia.org/wiki/Big_Rip
George
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Date: 18 Jul 2007 00:49:53
From: Crown-Horned Snorkack
Subject: Re: How long will the sun remain a white dwarf?
|
On 16 juuli, 19:08, Chris L Peterson <c...@alumni.caltech.edu > wrote:
> On Mon, 16 Jul 2007 08:39:07 -0700, Crown-Horned Snorkack
>
> <chornedsnork...@hush.ai> wrote:
> >Would there ever be a time when the emitted heat of the white dwarf is
> >significantly less than incident relict radiation? The white dwarf is
> >cooling, but so is relict radiation...
>
> Unless you can propose some active cooling mechanism (that is, something
> other than passive radiation), it would violate the second law of
> thermodynamics for the white dwarf to become cooler than the temperature
> of the Universe as measured from the white dwarf's location (which in
> all likelihood will be very close to the average relict radiation
> temperature).
>
> The white dwarf will remain forever warmer than the background.
>
And Earth is forever warmer than background. However, geothermal heat
is negligible compared to incident light of Sun.
Would the white dwarf cool to a point where its loss of internal heat
is smaller than the incident relict radiation?
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Date: 18 Jul 2007 14:34:41
From: Chris L Peterson
Subject: Re: How long will the sun remain a white dwarf?
|
On Wed, 18 Jul 2007 00:49:53 -0700, Crown-Horned Snorkack
<chornedsnorkack@hush.ai > wrote:
>And Earth is forever warmer than background. However, geothermal heat
>is negligible compared to incident light of Sun.
Not so. The Earth gives up more heat than it receives from the Sun. It
is slowly cooling. The Sun provides nowhere near enough energy to heat
the Earth above its current temperature. Don't confuse the temperature
of the Earth as a whole, which is determined by residual heat of
formation and by internal radioactive processes, with the surface and
atmospheric temperature, which is determined largely by solar radiation.
>Would the white dwarf cool to a point where its loss of internal heat
>is smaller than the incident relict radiation?
Again, that would violate the second law. Heat flows from warm to cold,
not the other way. The white dwarf will spend eternity with its
temperature asymptotically approaching its surrounding temperature. It
can never get colder than the background, unless some cosmic
refrigerator comes along and actively pumps heat out of it.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 20 Jul 2007 09:12:35
From: Paul Schlyter
Subject: Re: How long will the sun remain a white dwarf?
|
In article <fk8s93h53qo1i3r457n9hq0cpbo6460tne@4ax.com >,
Chris L Peterson <clp@alumni.caltech.edu > wrote:
> On Wed, 18 Jul 2007 00:49:53 -0700, Crown-Horned Snorkack
> <chornedsnorkack@hush.ai> wrote:
>
>> And Earth is forever warmer than background. However, geothermal heat
>> is negligible compared to incident light of Sun.
>
> Not so. The Earth gives up more heat than it receives from the Sun. It
> is slowly cooling. The Sun provides nowhere near enough energy to heat
> the Earth above its current temperature. Don't confuse the temperature
> of the Earth as a whole, which is determined by residual heat of
> formation and by internal radioactive processes, with the surface and
> atmospheric temperature, which is determined largely by solar radiation.
....which means the geothermal heat flow is negligible compared to
the radiation heat flow from the Sun onto the Earth, and from the Earth
out into speace. Or else, geothermal heat would need to be taken into
account by meteorologists when forecasting the weather.
Only on small parts of the Earth (e.g. on Iceland), geothermal heat flow
is non-negligible on the Earth's surface.
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
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Date: 20 Jul 2007 13:26:46
From: Chris L Peterson
Subject: Re: How long will the sun remain a white dwarf?
|
On Fri, 20 Jul 2007 09:12:35 GMT, pausch@saaf.se (Paul Schlyter) wrote:
>....which means the geothermal heat flow is negligible compared to
>the radiation heat flow from the Sun onto the Earth, and from the Earth
>out into speace...
Good thing, too, since the average (bulk) temperature of the Earth is
well over 3000°C. Talk about global warming! We're protected by a nice,
insulating crust.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 16 Jul 2007 08:39:07
From: Crown-Horned Snorkack
Subject: Re: How long will the sun remain a white dwarf?
|
On 13 juuli, 22:45, Radium <gluceg...@gmail.com > wrote:
> Hi:
>
> When the sun becomes a white dwarf, approximately how long will it
> take for it to cool off to a cold black dwarf that does not emit
> anymore heat or light [or other energies] than the surrounding space?
>
> Thanks,
>
> Radium
Would there ever be a time when the emitted heat of the white dwarf is
significantly less than incident relict radiation? The white dwarf is
cooling, but so is relict radiation...
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Date: 16 Jul 2007 16:08:28
From: Chris L Peterson
Subject: Re: How long will the sun remain a white dwarf?
|
On Mon, 16 Jul 2007 08:39:07 -0700, Crown-Horned Snorkack
<chornedsnorkack@hush.ai > wrote:
>Would there ever be a time when the emitted heat of the white dwarf is
>significantly less than incident relict radiation? The white dwarf is
>cooling, but so is relict radiation...
Unless you can propose some active cooling mechanism (that is, something
other than passive radiation), it would violate the second law of
thermodynamics for the white dwarf to become cooler than the temperature
of the Universe as measured from the white dwarf's location (which in
all likelihood will be very close to the average relict radiation
temperature).
The white dwarf will remain forever warmer than the background.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 15 Jul 2007 16:55:32
From:
Subject: Re: How long will the sun remain a white dwarf?
|
Paul Schlyter wrote: (snip)
Paul please read the following references in order to
improve the quality of your posts::
Quoting Style in Newsgroup Postings
http://www.xs4all.nl/%7ewijnands/nnq/nquote.html
How do I quote correctly in usenet?
http://www.netmeister.org/news/learn2quote2.html
Common Mistakes in Usenet Postings and How to Avoid Them
http://www.complang.tuwien.ac.at/anton/mail-news-errors.html#quoting
Bottom vs. top posting and quotation style on Usenet
http://www.cs.tut.fi/~jkorpela/usenet/brox.html
Why bottom-posting is better than top-posting
http://www.caliburn.nl/topposting.html
+What do you mean "my reply is upside-down"?
http://www.i-hate-computers.demon.co.uk/quote.html
Put an end to Outlook Express's messy quotes with this automated fix!
http://home.in.tum.de/~jain/software/oe-quotefix/
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Date: 18 Jul 2007 13:53:32
From: George 'Dubya' Bush the Second
Subject: Re: How long will the sun remain a white dwarf?
|
What was wrong with his post? Considering the quality of the content
of most posts on Usenet his was 98% above most.
On Sun, 15 Jul 2007 16:55:32 +0000, invalid@example.com wrote:
>
>
>
>Paul Schlyter wrote: (snip)
>
>Paul please read the following references in order to
>improve the quality of your posts::
>
>Quoting Style in Newsgroup Postings
>http://www.xs4all.nl/%7ewijnands/nnq/nquote.html
>
>How do I quote correctly in usenet?
>http://www.netmeister.org/news/learn2quote2.html
>
>Common Mistakes in Usenet Postings and How to Avoid Them
>http://www.complang.tuwien.ac.at/anton/mail-news-errors.html#quoting
>
>Bottom vs. top posting and quotation style on Usenet
>http://www.cs.tut.fi/~jkorpela/usenet/brox.html
>
>Why bottom-posting is better than top-posting
>http://www.caliburn.nl/topposting.html
>
>+What do you mean "my reply is upside-down"?
>http://www.i-hate-computers.demon.co.uk/quote.html
>
>Put an end to Outlook Express's messy quotes with this automated fix!
>http://home.in.tum.de/~jain/software/oe-quotefix/
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Date: 14 Jul 2007 08:35:00
From: Havriliak@aol.com
Subject: Re: How long will the sun remain a white dwarf?
|
Don'tforget about fluctuation theory, sometimes known as Statistical
Mechanics. You will et a time (in that time range) where the
probability is that once heated water is colder than the ice.
On Jul 14, 5:42?am, pau...@saaf.se (Paul Schlyter) wrote:
> In article <1184355936.720567.167...@o11g2000prd.googlegroups.com>,
>
> Radium <gluceg...@gmail.com> wrote:
> > When the sun becomes a white dwarf, approximately how long will it
> > take for it to cool off to a cold black dwarf that does not emit
> > anymore heat or light [or other energies] than the surrounding space?
>
> SInce the cooloff is pretty much exponential, it will take forever and
> the rediated energy will never drop to exactly zero. SO you should
> rephrase your question as:
>
> # When the sun becomes a white dwarf, approximately how long will it
> # take for it to cool off to a cold black dwarf that does not emit
> # any significant anounts of heat or light [or other energies] than
> # the surrounding space?
>
> That time span will depend a lot on your precise definition of
> "significant". But it will probably take hundreds of billion years,
> or more.
>
> Let me give you one concrete example: suppose the outside temperature
> is exactly freezing, i.e. 0 deg C. You boil a pot of water, then
> bring it outside. How long time will it take until the pot has
> cooled down so there's no temperature difference between the pot
> of water and the surroundings?
>
> At the start, the temperature difference is 100 deg C of course.
> Let's say after one hour the temperature difference is 10 degrees.
> After two hours it's 1 degree, after three hours 0.1 degrees, after
> four hours 1E-2 degrees. After a day+night the temperature difference
> is 1E-22 degrees, after a week 1E-166 degrees, after a year 1E-8764
> degrees, and after 15 billion years 1E-131490000000000 degrees. The
> temperature difference will never ever go all the way to zero!
>
> Of course a temperature difference of 1E-6 degrees or smaller is
> indistinguishable from zero - we call such a difference insignificant.
>
> But where do you draw the line between "significant" and
> "insignificant" here? In the example above, do you consider the
> temperature of the pot of water to be "the same" as the surroundings
> when the temperature difference drops below one degree? If so, it
> will happen after two hours. Or do you require a temperature
> difference of less than 0.01 degrees to consider the temperatures "the
> same"? If so, the cooldown will require four hours.
>
> The situation is similar with a white dwarf: no internal fusion gives
> any energy anymore, so the white dwarf just cools down. OK, there's
> one internal energy source remaining: gravitational contraction: the
> white dwarf can contract somewhat under its own gravitation, and that
> will release some energy, keeping it warmer for some time(*). But
> still the white dwarf cools off more or less exponentially. Now,
> since the white dwarfs are faint stars, they don't radiate that much
> energy out into space, and that's one major reason they can "live" for
> so long.
>
> (*) Before astronomer's realized that the Sun's energy source was nuclear
> fusion, other sources of energy were suggested. If the Sun had been
> a huge coal fire, it would be able to shine only for a few centuries,
> maybe a millennium. A more efficient energy source was gravitational
> contraction, which would be able to keep the Sun hot for approximately
> a million years. Back then, geologists suggesting that the Earth is
> some 5 billion years old had an obvious difficulty: what energy source
> could have kept the Sun shining for those five billion years? The
> answer is of course nuclear fusion - but it wasn't until well into the
> 1900's that astronomers realized this.
>
> --
> ----------------------------------------------------------------
> Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
> e-mail: pausch at stockholm dot bostream dot se
> WWW: http://stjarnhimlen.se/
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Date: 14 Jul 2007 09:42:18
From: Paul Schlyter
Subject: Re: How long will the sun remain a white dwarf?
|
In article <1184355936.720567.167930@o11g2000prd.googlegroups.com >,
Radium <glucegen1@gmail.com > wrote:
> When the sun becomes a white dwarf, approximately how long will it
> take for it to cool off to a cold black dwarf that does not emit
> anymore heat or light [or other energies] than the surrounding space?
SInce the cooloff is pretty much exponential, it will take forever and
the rediated energy will never drop to exactly zero. SO you should
rephrase your question as:
# When the sun becomes a white dwarf, approximately how long will it
# take for it to cool off to a cold black dwarf that does not emit
# any significant anounts of heat or light [or other energies] than
# the surrounding space?
That time span will depend a lot on your precise definition of
"significant". But it will probably take hundreds of billion years,
or more.
Let me give you one concrete example: suppose the outside temperature
is exactly freezing, i.e. 0 deg C. You boil a pot of water, then
bring it outside. How long time will it take until the pot has
cooled down so there's no temperature difference between the pot
of water and the surroundings?
At the start, the temperature difference is 100 deg C of course.
Let's say after one hour the temperature difference is 10 degrees.
After two hours it's 1 degree, after three hours 0.1 degrees, after
four hours 1E-2 degrees. After a day+night the temperature difference
is 1E-22 degrees, after a week 1E-166 degrees, after a year 1E-8764
degrees, and after 15 billion years 1E-131490000000000 degrees. The
temperature difference will never ever go all the way to zero!
Of course a temperature difference of 1E-6 degrees or smaller is
indistinguishable from zero - we call such a difference insignificant.
But where do you draw the line between "significant" and
"insignificant" here? In the example above, do you consider the
temperature of the pot of water to be "the same" as the surroundings
when the temperature difference drops below one degree? If so, it
will happen after two hours. Or do you require a temperature
difference of less than 0.01 degrees to consider the temperatures "the
same"? If so, the cooldown will require four hours.
The situation is similar with a white dwarf: no internal fusion gives
any energy anymore, so the white dwarf just cools down. OK, there's
one internal energy source remaining: gravitational contraction: the
white dwarf can contract somewhat under its own gravitation, and that
will release some energy, keeping it warmer for some time(*). But
still the white dwarf cools off more or less exponentially. Now,
since the white dwarfs are faint stars, they don't radiate that much
energy out into space, and that's one major reason they can "live" for
so long.
(*) Before astronomer's realized that the Sun's energy source was nuclear
fusion, other sources of energy were suggested. If the Sun had been
a huge coal fire, it would be able to shine only for a few centuries,
maybe a millennium. A more efficient energy source was gravitational
contraction, which would be able to keep the Sun hot for approximately
a million years. Back then, geologists suggesting that the Earth is
some 5 billion years old had an obvious difficulty: what energy source
could have kept the Sun shining for those five billion years? The
answer is of course nuclear fusion - but it wasn't until well into the
1900's that astronomers realized this.
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
|
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Date: 15 Jul 2007 16:04:56
From: Guy Macon
Subject: Re: How long will the sun remain a white dwarf?
|
Paul Schlyter wrote:
>At the start, the temperature difference is 100 deg C of course.
>Let's say after one hour the temperature difference is 10 degrees.
>After two hours it's 1 degree, after three hours 0.1 degrees, after
>four hours 1E-2 degrees. After a day+night the temperature difference
>is 1E-22 degrees, after a week 1E-166 degrees, after a year 1E-8764
>degrees, and after 15 billion years 1E-131490000000000 degrees. The
>temperature difference will never ever go all the way to zero!
This assumes that the quantum of temperature is smaller than
10^-131490000000000 degrees...
--
Guy Macon <http://www.guymacon.com/ >
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Date: 14 Jul 2007 01:33:10
From: William Hamblen
Subject: Re: How long will the sun remain a white dwarf?
|
On Fri, 13 Jul 2007 19:45:36 -0000, Radium <glucegen1@gmail.com >
wrote:
>When the sun becomes a white dwarf, approximately how long will it
>take for it to cool off to a cold black dwarf that does not emit
>anymore heat or light [or other energies] than the surrounding space?
It takes a solar type star about 100 billion years, which is more than
the presently estimated age of the universe.
Bud
--
The night is just the shadow of the Earth.
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Date: 13 Jul 2007 21:42:41
From: Radium
Subject: Re: How long will the sun remain a white dwarf?
|
On Jul 13, 1:16 pm, Chris L Peterson <c...@alumni.caltech.edu > wrote:
> That would take forever. But a few tens of billions of years should be
> long enough that the temperature drops low enough that no photons in the
> visible range are produced, which is generally what defines a black
> dwarf.
Approximately how long until this white drawf [which used to be the
sun] cools to around 70 degrees Fahrenheit? Will the universe exist
long enough for this to happen?
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Date: 14 Jul 2007 05:03:50
From: Chris L Peterson
Subject: Re: How long will the sun remain a white dwarf?
|
On Fri, 13 Jul 2007 21:42:41 -0700, Radium <glucegen1@gmail.com > wrote:
>Approximately how long until this white drawf [which used to be the
>sun] cools to around 70 degrees Fahrenheit? Will the universe exist
>long enough for this to happen?
The temperature falls off somewhat exponentially... looks like it would
take hundreds of billions of years to get that cool, maybe trillions.
But it has all the time in the world (or the Universe), since it seems
likely the Universe will not ever cease to exist, but will just keep
cooling down and expanding forever.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 14 Jul 2007 04:59:56
From: Sam Wormley
Subject: Re: How long will the sun remain a white dwarf?
|
Radium wrote:
> On Jul 13, 1:16 pm, Chris L Peterson <c...@alumni.caltech.edu> wrote:
>
>> That would take forever. But a few tens of billions of years should be
>> long enough that the temperature drops low enough that no photons in the
>> visible range are produced, which is generally what defines a black
>> dwarf.
>
> Approximately how long until this white drawf [which used to be the
> sun] cools to around 70 degrees Fahrenheit? Will the universe exist
> long enough for this to happen?
>
The Cooling of CO White Dwarfs: Influence of the Internal Chemical Distribution
http://www.journals.uchicago.edu/ApJ/journal/issues/ApJ/v486n1/34903/34903.html
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Date: 13 Jul 2007 20:16:43
From: Chris L Peterson
Subject: Re: How long will the sun remain a white dwarf?
|
On Fri, 13 Jul 2007 19:45:36 -0000, Radium <glucegen1@gmail.com > wrote:
>Hi:
>
>When the sun becomes a white dwarf, approximately how long will it
>take for it to cool off to a cold black dwarf that does not emit
>anymore heat or light [or other energies] than the surrounding space?
That would take forever. But a few tens of billions of years should be
long enough that the temperature drops low enough that no photons in the
visible range are produced, which is generally what defines a black
dwarf.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
|
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Date: 14 Jul 2007 09:42:19
From: Paul Schlyter
Subject: Re: How long will the sun remain a white dwarf?
|
In article <d2nf9391k03rnq48ejansavkuqltrgipdq@4ax.com >,
Chris L Peterson <clp@alumni.caltech.edu > wrote:
> On Fri, 13 Jul 2007 19:45:36 -0000, Radium <glucegen1@gmail.com> wrote:
>
>>Hi:
>>
>>When the sun becomes a white dwarf, approximately how long will it
>>take for it to cool off to a cold black dwarf that does not emit
>>anymore heat or light [or other energies] than the surrounding space?
>
> That would take forever. But a few tens of billions of years should be
> long enough that the temperature drops low enough that no photons in the
> visible range are produced, which is generally what defines a black
> dwarf.
That would take forever too!!! According to the Planck blackbody
radiation curve, any blackbody hotter than absolute zero radiates
photons over all wavelengths. Yes, you and I radiate visible light,
X-rays and even gamma rays, although at an extremely low rate - but
still at a rate slightly above zero. And if a cool body would emit,
say, one gamma ray photon over a billion years, is that "no gamma
radiation" or not?
So if you say "that would take forever" about cooling down until no
more energy is radiated, you must say the same about radiation at
visible wavelengths, or any other wavelength rate. Only if you set some
level near but above sero as "insignificant" you can assign a finite
cooldown time span.
>
> Chris L Peterson
> Cloudbait Observatory
> http://www.cloudbait.com
--
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Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
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Date: 14 Jul 2007 14:04:10
From: Chris L Peterson
Subject: Re: How long will the sun remain a white dwarf?
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On Sat, 14 Jul 2007 09:42:19 GMT, pausch@saaf.se (Paul Schlyter) wrote:
>That would take forever too!!!
That's true. I meant until the level of visible photons drops below
detectability (which is, of course, a moving target). As you say, all
that can be done is to set a threshold, or a specific target
temperature.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 14 Jul 2007 16:46:36
From: George Dishman
Subject: Re: How long will the sun remain a white dwarf?
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"Chris L Peterson" <clp@alumni.caltech.edu > wrote in message
news:rplh93973ll761k6cgsnpufj37n1qvtnck@4ax.com...
> On Sat, 14 Jul 2007 09:42:19 GMT, pausch@saaf.se (Paul Schlyter) wrote:
>
>>That would take forever too!!!
>
> That's true. I meant until the level of visible photons drops below
> detectability (which is, of course, a moving target). As you say, all
> that can be done is to set a threshold, or a specific target
> temperature.
I think the OP asked about 70F with the idea of having
some humans around. His question is really whether there
could be habitable planets around at a time when the
galaxies were evaporating rather than how long it would
take for a white dwarf to cool to 290K.
One can imagine a time when gathering hydrogen to keep
their brown dwarf running was a civilisation's main
occupation, but I guess that's another story.
George
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Date: 13 Jul 2007 20:07:27
From: Sam Wormley
Subject: Re: How long will the sun remain a white dwarf?
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Radium wrote:
>
> When the sun becomes a white dwarf, approximately how long will it
> take for it to cool off to a cold black dwarf that does not emit
> anymore heat or light [or other energies] than the surrounding space?
>
The Cooling of CO White Dwarfs: Influence of the Internal Chemical Distribution
http://www.journals.uchicago.edu/ApJ/journal/issues/ApJ/v486n1/34903/34903.html
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