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Author Topic: Can you tell me about degenerate matter?  (Read 3426 times)

Offline Supercryptid

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Can you tell me about degenerate matter?
« on: 15/12/2010 22:10:42 »
I know what degenerate matter is. I'm just curious about some of its properties.

Let's imagine that we have a black dwarf. I guess we'll say it's the same temperature as the background of space (i.e. very cold). Now I'm wondering about the properties of this degenerate matter.

Does this matter have a "crystalline" strucure? What I mean is, does it have a regular repeating structure like that which might be found with crystalline matter on Earth? If not, might it be a glass? I realize it doesn't have chemical bonds as we know them on Earth, but it seems like there should be a pattern to the way the atoms are arranged. Perhaps they are arranged in the tightest possible way; hexagonal close-packing or cubic close packing?

Is it a conductor or an insulator? It doesn't have chemical bonds as we have on Earth, so I don't know which one it would likely be.

Does it have friction? Seems like a black dwarf would have an extremely smooth surface due to the very high gravity and tight spacing of the atoms. Would it be frictionless? Just low friction?

Is it opaque, transparent, etc.? How would it interact with light?

Any information would be good enough, thanks.


 

Offline Soul Surfer

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Can you tell me about degenerate matter?
« Reply #1 on: 15/12/2010 23:51:35 »
Truly cold degenerate matter does not exist in our universe yet because there has not been time for a white dwarf star to cool down.  This will take many times the current age of the universe to happen.

Some of the words you use suggest that you may not know as much about degenerate matter as you suggest so I will start by defining it.

Degenerate matter is a plasma of ionised atoms compressed by strong gravity so that the normal electron structure of the isolated atom is crushed by the pressure of the layers of the star above and the structure of the star is maintained by the electron degeneracy pressure rather than the standard gas pressure that applies to normal material.  This applies to white dwarf stars but it is not used for neutron stars which are altogether more compressed objects.  To give an idea of scale  a white dwarf with the mass of the sun is about as big as the earth whereas a neutron star with the mass of the sun is about as big as a city say a few miles across and about 3-5 times as big as a black hole of the same mass.

I have never seen any description about what a cold white dwarf would be like but I can generate some ideas from the information available.  firstly there would be an outer crust of and atmosphere of normal gas and atoms.  These are likely to be mostly helium but there could be some carbon and oxygen and other light atoms but there would not be much in the way of heavier atoms like iron and beyond because these do not form in the lighter stars like the sun that develop into white dwarves.  There would be some but not very much hydrogen because this is in effect the cinder core of a burnt out star in which most of the hydrogen has been fused or blown off with the outer atmosphere during its asymptotic giant phase (QV).  Beneath that there will be a layer of partially ionised degenerate matter (i.e. there may be some electrons still attached to the nuclei leading to a core of fully degenerate matter.  This is a plasma and does not have a fixed structure so it could be in effect a gas although it may at low temperatures develop medium range order like a liquid.  It would be conducting and possibly even superconducting and so the star could develop a magnetic field.

I am not sure if this material could develop superfluidity.

The material would be very opaque to light and most electromagnetic radiation up to extreme energies but would not be opaque to neutrinos
« Last Edit: 15/12/2010 23:56:26 by Soul Surfer »
 

Offline Supercryptid

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Can you tell me about degenerate matter?
« Reply #2 on: 16/12/2010 05:58:27 »
One of the things I found curious was the claim that a white dwarf was found which was made of "diamond". I know it can't be ordinary diamond due to the extreme pressures. This seems to indicate the white dwarves (and therefore black dwarves) would contain solid degenerate matter (at least in their cores:

http://www.spacetoday.org/DeepSpace/Stars/WhiteDwarfs/LucyDiamondStarWhiteDwarf.html
 

Offline Soul Surfer

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Can you tell me about degenerate matter?
« Reply #3 on: 16/12/2010 09:50:54 »
Yes I remember that article coming out now.  I dismissed as standard science journalistic Hype and a total load of rubbish even though it did contain a few useful facts.  I wish science journalism would not do things like this I believe it does more harm than good to the cause of science.    It does point out a possibility that I did not consider in my first explanation that the cores of white dwarves could be substantially one nuclear type or layered because that was the stage the star got to when it blew away its outer layers as an asymptotic giant becoming a planetary nebula in the process.

I agree that it could not possibly be conventional diamond because the density is so high, but the structure could possibly be similar.  It is interesting to consider that it is a solid because it must be very hot inside.  I am sure that some of the electrons will be mobile so it would be a form of metallic carbon.

To decide that it was a solid this pulsating star must show shear waves as well as compression waves because liquids do not show shear waves.  Although models and observations are limited at this distance a lot of the relevant information needed to build the star is available from the spectrum but a good estimate of the distance is also needed but this could come from pother sources.
 

Offline granpa

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Can you tell me about degenerate matter?
« Reply #4 on: 17/12/2010 03:28:08 »

 

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