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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 An exemplary answer Mr. Tung ;-) I only wish I'd written that in my last exam ;-( jc |
#12
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When the sun becomes a white dwarf why will it take SO long tocool off?
Besides being degenerate, white dwarf are mostly carbon
and oxygen. Ideal places to saearch for extra-terrestrial life in fact ? -- Boo |
#13
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When the sun becomes a white dwarf why will it take SO long tocool off?
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. |
#14
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When the sun becomes a white dwarf why will it take SO long tocool off?
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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When the sun becomes a white dwarf why will it take SO long to cool off?
So there are not any stone cold dead white dwarfs? |
#16
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When the sun becomes a white dwarf why will it take SO long to cool off?
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 |
#17
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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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When the sun becomes a white dwarf why will it take SO long 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 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 |
#19
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When the sun becomes a white dwarf why will it take SO long tocool off?
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/sc...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/phys...yPressure.html |
#20
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When the sun becomes a white dwarf why will it take SO long to cool off?
So are they diamonds yet? And if so, what would they radiate or reflect being diamonds? |
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