Why would neutron degenerate matter come apart if released from pressure?

Hi, I got curious about neutron stars by way of gamma ray bursters, from my reading I learned that they're composed primarily of a fluid of neutron degenerate matter (NOT going to use word neutronium-has fuzzy definition)

neutron degeneracy pressure (from Pauli exclusion principle) keeps NDM from compressing indefinitely unless the gravity field is great enough to form a black hole

free neutrons decay into a proton and a electron in about 10-15 mins

Neutronium of science fiction fame is just a bunch of hooey (too bad, kind of a cool idea)

Wikipedia (great site btw) says that if pressure is released the NDM would explode with extreme force.

My question is:

Why would it explode? I can understand some rebound from the pressure, but why would the individual neutrons disassociate from each other, wouldnt the neutrons still be bound to each other via the residual strong force? I would think that if the pressure were released gradually it would be okay.

What am I missing?

Thanks

 

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I guess it would explode for the same reason that heavy atomic nucleii decay explode (decay) - the weak nuclear force, right?

 

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I suppose what happens inside a neutron star depends on which theory/interpretation one favors since what actually happens is unknown. I don't think either a strong force or weak force would still exist in the neutron star core though. The iron atom's electrons are compressed into the nuclei, which then combine with the protons to form, uh, something that is still sometimes referred to as neutronium. This neutronium is unstable, however, so a 'shield' or some such could not be made from the material. It may be some type of 'quark soup'. Some theories describe a scenario in which the individual neutrons break down into their constituent quarks, which bind together in a sufficiently massive neutron star. This is supposed to form a stable 'strange star' which is composed of 'strange matter'. 'Strangelets' are pieces of this strange star, which can exist on their own outside the pressures of the star, in all different sizes. Even atom-sized ones are stable, unlike tiny black holes. Like a black hole, the gravity of a strangelet is so intense that it would 'eat' any ordinary matter it came into contact with, even planets! I have no idea if such things can exist, but they are interesting, huh?

 

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this is the part you are missing....

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and there is more.

-MT

 

Are there any links to strangelet stars?

 

Here is a cut & paste from wiki and a link to the page there. There are several external links, but I have not looked at them to see what they contain. I had seen the term 'strangelet' a couple of times, and when I read the thread in which Paul Dixon mentioned them, I decided to find out what they were. This was a year or so ago and I don't have specific links without searching. Maybe the following will get you started in the right direction:

http://en.wikipedia.org/wiki/Quark_star

 

would it be possible to have a nuetron star with a quark core?

 

I think that in most theories, neutron stars do have a quark core. Remember, there are THREE kinds of quarks, up quark, down quark and strange quark. Ordinary matter is made up of up and down quarks. I think some models predict regular neutron stars may have a core composed of up and down quarks. The strange quark is much heavier and more stable than the other flavors, and is the particle that strange stars are theorized to be composed of. Strangelets are 'pieces' of a strange star, extremely dense and stable objects exibiting enough gravitational attraction to destroy ordinary matter that comes too close, similiar to a black hole.

 

When you say destroy, do you mean convert to strange matter or do you mean compress down to neutron degenerate matter

 

My understanding from what I have read is that a strangelet would absorb ordinary matter by accretion, the same as a black hole, adding to its own mass. You do have to realize that matter would have to be VERY close to a small strangelet for accretion to take place. Gravity decreases by the inverse square of distance, so the strangelet could presumably not 'suck in' matter from very far away. Also remember these are theorized particles and objects. The exact description of their properties, if they are real particles, is not yet known. You can read Dr. Wagner's post in the 'Supernova from experimentation' thread. I have only a very basic knowledge of strangelets garnered from reading a few papers. I don't know if he would be willing to go into detail about the theories, but I know he has a much, much greater knowledge of them than I.

 

Strangelet theory is well-developed, but still just theory. Google on "strangelets" and you'll find lots of articles. Searches for strangelets at the RHIC, and at its predecessor (which is now the RHIC injector) have resulted in no evidence for the existence of positively or negatively charged strangelets. Neutral strangelets cannot be detected by the detectors.

Strangelets of low mass (3-5 amu) are posited to be 'highly radioactive', i.e. stable for a while, but able to decay back to normal matter. Strangelets are named as such because they are posited to have an excess of strange quarks, which serves to stabilize them, making them more stable than normal nuclear matter.

Once their mass exceeds several dozen or so amu, they are no longer 'radioactive'. Unlike normal matter, which has coulombic repulsion making the nuclei unstable beyond a charge of about 90, strange matter nuclei become increasingly more stable as the mass increases, even if electric charge is present. It is that property which would allow for a large strangelet to continue to accrete normal matter (if it got past a coulombic penetration barrier on a charged strangelet nucleus, which would be present on positive/negative strangelets, but not on neutral strangelets - not an impossibility since the fusion potential is far greater than for normal matter, in which spontaneous fusion of normal matter Deuterium-Tritium in fact takes place, albeit at a VERY low rate circa 1 fusion/second/1E26 atoms), growing ever larger as it encountered more and more normal-matter atoms, which would be accreted, followed by a charge emission ('burp') to keep the charge in line with theory.

The accretion, however, should not exponential like in a nuclear bomb (which allows for a rapid chain-reaction of doubling every nano-second or so), but rather more like a linear accretion, so that it would take literally millions of years for a single strangelet produced to become a strange atom of some 6E23 amu (1 gram). Mass production, (over several years of thousands of beam-runs) of millions of strangelets at the forthcoming LHC might be a problem, if strangelets are real, and not just theory.

For the spontaneous fusion of Deuterium-Tritium, Scientific Amercian had an interesting article (by Physicist Steve Jones at BYU circa 1987) on muon-induced fusion, in which muons inserted into a Deuterium-Tritium mixture replaced the electrons, shortening the covalent-bonding of the two nuclei in the D-T molecule just enough to allow the spontaneous fusion to increase tremendously. On the order of some 137 fusions would take place for each introduced muon, before the muon decayed or left the system. That was not enough, however, to make the system practical.

Whether strangelets (or strange stars in lieu of neutron stars) are real remains to be seen.

 

Thank you, that was both highly interesting and informative.

 

ITS A SIMPLE QUESTION... are the bound nuetrons in nuetron stars.. cold? or hot?

do they have energy?
or
do they lack energy?

some, like 'dr. manuel'... say, they have exess energy.. 200 million ev worth each.

thats why they can explode.....

-MT

 

i've heard that neutron stars rotate very fast, if it's true, why do they do that? i get the feeling that by rotating they try to keep themselves from dying/exploding, by throwing away some of their energy (mass?).

 

Neutron stars spin fast because of conservation of angular momentum, think about it, the orginal star is anywhere from 6090000 miles (blue giant) to 15225000 miles wide and all rotate, after it supernovas (which can also impart angular momentum) the remnant shrinks down to 20 kilometers (12 miles), its still got all or most of its original angular momentum so the dense little ball has to spin incredibly fast.

Its like a figure skater drawing their arms in while they spin, as their arms draw in they speed up.

Eventually over huge time scales a neutron star slows down, usually due to drag on the intestellar medium by the neutron stars magnetic field, it can also slow down if it is ejecting a jet of matter off center from its pole and shed momentum that way (unlikely though)

 

Hi Maast

A neutron star is a delicate balancing act between gravity pushing inwards and pressure pushing outwards. IN this case the pressure is supplied by two sources:
i) neutron degeneracy pressure
ii) the strong nuclear force

(i) is a pressure due to the motion of particles very tightly confined by pauli exclusion. (ii) is due to the strong force actually becoming repulsive at or around the nuclear density barrier. If you relieve the inward push by removing the gravity then there is nothing to oppose the pressures and so the star will fly apart.

Hope this helps!
MC

 

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Good to see you again, Chris. Will this be another hit and run, or would you like to stay around for a while?

I'm going to dredge up an old question about wormholes that I'm hoping you can answer for me.

 

Hi Pete

I'll be here while I have time and the interest sustains me.

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James! My man. Good to see you again. How's the wife?