Degenerate matter and metals

General physics and astronomy discussions not directly related to Celestia

What is the best definition of degenerate matter in your opinion? (Note: by densimetal I mean white dwarf material and alike)

1 - Any matter that has a degenerate fermi gas of free particles. (eg. metals, metallic hydrogen, densimetals, neutronium, strange matter)
0
No votes
2 - Any matter subject to pressures high enough to cause pressure ionization or other changes. (eg. metallic hydrogen, densimetals, neutronium, strange matter)
0
No votes
3 - Matter compressed enough to be totally ionized or to suffer other modifications, such as neutronization (eg. totally ionized densimetals, neutronium, strange matter)
1
25%
4 - Only the degenerate fermions. (Eg: for a white dwarf densimetal, only the electrons constitute a degenerate matter (since free neutrons, protons and nuclides are not degenerate); for metals, only the conduction electrons)
1
25%
5 - A not very well defined term.
0
No votes
6 - None of the above.
2
50%
 
Total votes: 4

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maaf
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Degenerate matter and metals

Post #1by maaf » 20.05.2004, 02:01

I would like to know if is there any precise definition for the expression " degenerate matter". Is "degenerate matter" some not very well defined term, like " thermal energy", that is avoided in more advanced textbooks in Astrophysics or does it has a very precise definition?

I would like to know if it's ok to consider ordinary metals (e.g a iron bar or a chunk of aluminum at 1 atm) a kind of degenerate matter (or more or less a sort of "electron degenerate matter" ). Or this would be to force too much the definition of degenerate matter to include metals?

P.S: densimetal is a term I've created for a matter subject to pressures high enough to cause the electrons to be stripped from the atoms, thus making atoms pressure ionized. Examples include "white dwarf matter" and "metallic hydrogen" found at the core of gas giants and brown dwarfs. I used this term in the poll and here because its shorter than "white dwarf matter".

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Reasons to consider ordinary metals as a "sort of degenerate matter" includes:
- Both metals and densimetals have a degenerate electron gas, which gives them good thermal and electrical conductivities.
- In both metals and densimetals the atoms are ionized, although atoms in metals are little ionized and in densimetals atoms may be fully ionized.
- Both metals and densimetals have liquid and solid states (also know as liquid plasma and solid plasma for densimetals), with a clear phase transition between these two states.
All these makes in a sense ordinary metals (in solid and liquid states) more similar to densimetals ("white dwarf matter") than to non-metals.

Reasons to not consider ordinary metals as "degenerate matter":
- In ordinary metals the degeneracy pressure from the degenerate electrons is not always the dominant source of pressure.
- For a given pressure, the number density for densimetals is possibly nearly the same. This doesn't hold true for ordinary metals.
- Perhaps to avoid confusion of planets with degenerate stars.

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P.S: I don't want to modify existing terms or create more confusion, I just want to make the things clear or help to create more clear definitions.

Best Regards,
M?rcio

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Post #2by Evil Dr Ganymede » 20.05.2004, 08:13

I wouldn't consider metals as "degenerate" at all. I thought degenerate matter was matter that was so compressed that the atoms have no spaces between them - any more pressure would force the electrons into the nucleus to make neutronium. Maybe that's wrong though...

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Post #3by granthutchison » 20.05.2004, 09:46

This Wikipedia article on degenerate matter is admirably brief, very clear and addresses all your points.
Only the conducting electrons are degenerate in metals, so a metal's resistance to compression arises primarily from the electromagnetic interaction of more-or-less intact atoms, rather than degeneracy - the metal itself therefore cannot be described as degenerate. The exception is metallic hydrogen, which of course with one electron per atom is left without bound electrons when it becomes metallic, and therefore does rely on degeneracy pressure.

Grant

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Post #4by maaf » 20.05.2004, 16:04

I'm not sure if the definition at Wikipedia is a consensus in the Scientific Community or only the point of view of the author of the article. In fact, everybody can edit articles in Wikipedia and in some older versions of this article (Degenerate Matter), it was stated that Conventional Solids where a kind of degenerate matter. In the page
http://en.wikipedia.org/wiki/Degenerate_matter
click on "Page History" link to see the list of modifications.

So my doubts remain.

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Post #5by granthutchison » 20.05.2004, 16:16

maaf wrote:I'm not sure if the definition at Wikipedia is a consensus in the Scientific Community or only the point of view of the author of the article.
Sorry, I wasn't clear ... what I intended to imply in my last post was that, as far as I understand degenerate matter from other sources, the Wikipedia article is an accurate summary - I just gave the link as a quickly accessible reference, to save myself some writing. If you accept the definition of degenerate matter as being matter in which the Pauli exclusion principle is the prime contributor to resistance to compression (which seems to be generally accepted), then the rest of the Wikipedia article follows naturally and (I think) uncontroversially.

Grant

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Post #6by maaf » 22.05.2004, 16:33

Thanks granthutchison. You helped clearing this subject.

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Post #7by maaf » 23.05.2004, 00:57

I've found an interesting link about this subject:
http://cosmos.colorado.edu/stem/courses ... 5/l5S6.htm

Even though the author doesn't says that ordinary condensed matter is "degenerate matter", he points out that is the degeneracy pressure that prevents solids and liquids from being compressed, and that is due to "degeneracy pressure" that atoms doesn't collapse.
At the end of this page, the author points out that planets like Earth and Jupiter are also supported by degeneracy pressure.

P.S: This page belongs to a very introductory course in astronomy.

I did a search in a lot of sites about "degenerate matter", and it seems that the generally accepted definition for it is the definition given by Wikipedia or a similar definition (matter so much compressed that the atoms lost their electrons).

I also found out in some papers some folks trying to produce a "degenerate matter of atoms" with dilute gases at very low temperatures (potassium-40 at nanokelvins).

By the way. What do you think about the noun "densimetals" for white dwarf material? Any better suggestion?

Best Regards.

Topic author
maaf
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Classification of matter in increasing order of pressure:

Post #8by maaf » 25.05.2004, 03:36

Continuing my last thread posted in "Gas Giant Cores", I'm posting a classification of matter according to increased densities and pressures

Note: I'm not supposed to write to this forum now, since I have a lot of homework to do, but I got addicted.

Regardless of whether we classify some state of matter as "degenerate matter" or not, it remains the same. So perhaps is more useful to discuss it's properties than to discuss definitions (I think this is valid specially for myself)

To my understand, when we compress matter, say a sample of gaseus hydrogen at ambient temperatures, the following changes should occur:

gaseus molecular hydrogen => liquid molecular hydrogen (non-metallic) => semiconductor hydrogen => metallic hydrogen => densimetallic* hydrogen (non-relativistic degenerate electron gas) => densimetallic* hydrogen (relativistic degenerate electron gas) ==(neutronization)=> neutronium => strange matter => ?

For another sample, say oxygen:
gaseus molecular oxygen => liquid oxygen (non-metallic) => semiconductor oxygen => metallic oxygen (only outer electrons more or less free) => densimetallic* oxygen (partially pressure ionized, non - relativistic degenerate electron gas) => densimetallic* oxygen (fully ionized, non relativistic degenerate electron gas) => densimetallic* oxygen (fully ionized, relativistic degenerate electron gas) ==(neutronization)=> neutronium => strage matter => ?

For another sample, say pure sodium:
gaseus molecular sodium => metallic sodium (only outer electrons more or less free) => densimetallic* sodium (partially pressure ionized, non - relativistic degenerate electron gas) => densimetallic* sodium (fully ionized, non relativistic degenerate electron gas) => densimetallic* sodium (fully ionized, relativistic degenerate electron gas) ==(neutronization)=> neutronium => strage matter => ?

Some words about these stages of matter:

semiconductor => transition between non-metallic matter and mettalic matter, ocurring near the metallization pressure. (For ordinary non-metals, the metallization pressure is positive, for ordinary metals (eg. a chuck of aluminum at 1atm, 25 deg. Celsius) the metallization pressure is negative)

metals => Composed of a sea of free conduction electrons and positively charged ions (cations), little ionized. The free conduction electrons at ordinary temperatures (less than 10,000K) are degenerate. Although the degeneracy pressure of these free electrons contributes to support the matter against collapse due to negative coulombic pressure between electrons and nuclides, the pressure due to "interplay between the electrical repulsion of atomic nuclei and the screening of nuclei from each other by electrons allocated among the quantum states determined by the nuclear electrical potentials" is still very important. Although the free conduction electrons can be described as a degenerate electron gas, they are better described as a fermi-liquid. I would classify metals as a the first kind of "degenerate matter" found in increasing pressure order (perhaps with some reserves), since it has many similarities with densimetals. (Hence I would say that metallic elements have their outer electrons so weakly bonded that they form a kind of "degenerate matter" when they condense (it is, the negative coulombic pressure is enough, in a first approximation, to cause it's outer electrons to form a degenerate electron gas) ). But if my classification goes against an official definition of "degenerate matter" or if everybody disagrees, I may change my classification and classify ordinary metals as definitely not being "degenerate matter".

Note about densimetals: This is a name I'm proposing for matter found at extreme pressures, like the matter found inside white dwarfs and cold brown dwarfs, but not at pressures high enough to cause total "neutronization". This word is formed by "dense" + "metal", because the matter inside "white dwarfs" looks like metal (it has a large thermal and electrical conduction, plus being reflective) and is very dense. This name is still not official. My suggestion should be checked first by someone with deep knowledge about the subject, since I have only a superficial knowledge about this subject and I'm not even absolutely sure if the matter found inside white dwarfs have all these properties that makes it similar to a metal.
Densimetals is the first kind of matter that is usually regarded as a kind of degenerate matter, although I would classify both metals and densimetals as "degenerate matter of electrons" to highlight that in both exists a degenerate fermi gas composed of electrons that contribute to its internal pressure and gives them many similar bulk properties. (but again, I may change my classification if it goes against some other well stabilished definition for "degenerate matter").
I've been thinking about some mean to stabilish a boundary between the metallic and densimetallic regimes, but I don't have enough knowledge to do this. Perhaps one criteria could be when the density is big enough that the degeneracy pressure from the free electrons becomes dominant and the cations become small enough that the screening between cations become unimportant, in other words, when the number density of free electrons starts to depend only (I mean, be given only by) the pressure, with little relation to the chemical species composing the matter (carbon, oxygen, etc), if this really happens (which I don't know).
I belive that electrons in a densimetal are also precisely described as a Fermi liquid, like in metals, but since the densities in a densimetal are larger, the coulombic interactions are less important, so in densimetals the approximation for a degenerate electron fermi gas is even better than for metals.

P.S: I would be very happy if this term were adopted by the scientific community. But I'm open for suggestions and positive criticism.


Densimetals (partially ionized) => This type of matter is probably found in the interiors of low mass "white dwarfs" and in the core of cooled down "brown dwarfs", in this type of matter, the outer electrons from the atoms are ionized (pressure ionized), while the atom retains some of it's inner electrons. Some examples could include: "degenerate matter" of carbon, with carbon atoms with only two bond electrons (C++++ cation with a lot of e- forming a degenerate fermi gas). It's density should be between 100g/cm^3 up to the densities required to fully ionize the atoms.

Densimetals (fully ionized) => Increasing even further the pressure, the atoms become fully ionized. An exception for this is metallic hydrogen and densimetallic hydrogen, which is always fully ionized.

Densimetals (relativistic electron degenerate gas) => The pressure is so high, that electrons near the Fermi level have velocities very near to the speed of light. This kind of densimetal is only found inside white dwarfs.

neutronium => increasing the density even further, the electrons combine with protons, creating a state of matter know as neutronium, (even though this name is not widely accepted, due to uncertainities in the equation of state found at those incredible densities (see Wikipedia)).

I belive as when we increase the pressure over a sample of matter it should become first partially ionized (metallic state), if we increase the pressure further, it would become more ionized (densimetal (with partially ionized atoms). If we increase the pressure even further, all the electrons would become free (densimetal (with fully ionized atoms)). If we continue increasing the pressure, then the electrons near the Fermi level starts to behave relativistically (densimetal with relativistic electrons) with changes the equation of state of the degenerate electron gas. Increasing even more the pressure, the electrons begin to combine with protons, in a process named "neutronization" or "reverse beta decay". In this case, the pressure is so large that the matter becomes a sea of neutrons (neutronium), and a white dwarf star collapses to a neutron star.


Briefly, I would classify "degenerate matter" as:

"degenerate matter":
__"degenerate matter of electrons":
____metals
____densimetals
__"degenerate matter of nucleons"
____ neutronium
__"degenerate matter of quarks"
____strange matter.

But if the majority of you think this is leads to more confusion than to clear the subject out, I will change this classification and accept suggestions.

Some points that are still not clear to me (even though I've read the definition at Wikipedia thousands of times): (?????)
* Densimetals are "degenerate matter", but ordinary "metals" are definitely not degenerate matter (Give up maaf, you are definitely wrong).
* Even in densimetals, only the electrons should be regarded as being a degenerate matter?
* Every condensed matter could be regarded as "degenerate matter", since after, all is the Pauli exclusion principle that prevents atoms from collapsing.
* "Degenerate matter" is a not very well defined term.
Please somebody help.

Some caveats about my theory:

Oddly, when carbon is compressed, it changes from a partially conductive phase (graphite) to a totally non-metally, insulator phase (diamond), in the opposite way followed by most materials. (Remember that my theory is a gross simplification of what happens when we compress matter. Perhaps, compressing diamond even further, it becomes a kind of semicondutor diamond, and after a metallic diamont (perhaps at pressures found only inside brown dwarfs)).

Now it's done. I'll resume my discussion and thoughts about this when I finish all my homework. Bye for now

Topic author
maaf
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Post #9by maaf » 27.05.2004, 01:07

Thinking better, pehaps it's better to state that metals are not a kind of "degenerate matter". Thinking of a continuous transition from insulators to neutronium, as someone increases the pressure (and densities), we could state that metals are a kind of matter that is starting to become "degenerate matter". Ordinary metals is a kind of matter that just happens to be in this metallic state at near zero pressures (thus being "degenerate matter" to some extent at near zero pressures, but not enough to be qualified a kind of "degenerate matter")........ No. perhaps this is not so good either..... Perhaps it's better to state that "degenerate matter" is only the free electrons in both metals and densimetals......Perhaps even not this....... I'll have to study Quantum Mechanichs and perhaps Solid State Physics before I can state something for sure. An alternative would be to ask about this to an expert.

Best Regards,

I hope this hole discussion didn't bothered somebody.

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