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As the title says, what if a neutron star stops spinning what will happen to the materials that the neutron star is made of?

Will they still be super dense?

Are they brittle? If they are, how strong is it?

How heavy those materials will be?

Here's the actual scenario: A certain blacksmith discovers a rock (technically a mine) that is so heavy that in fact, just a pebble of it took him and 3 of his sons to carry it.

Along that scenario, what I could actually do with that kind of denseness and if it can be worked with.

Or possible create a fabric so strong that it beats other metals in terms of armor properties

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    $\begingroup$ Your estimate of neutron star density is way too low. Neutron stars weigh 100 thousand tons per cubic mm (roughly the size of a large grain of sand). $\endgroup$ – March Ho Jul 21 '16 at 11:39
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    $\begingroup$ Without the gravitational pressure holding it together, the degenerate matter of a neutron star will probably disinitgrate...by the particles flying away from each other at nearly the speed of light. $\endgroup$ – Thucydides Jul 21 '16 at 12:27
  • $\begingroup$ See this video for what a marble-sized piece of neutronium would do. $\endgroup$ – JDługosz Aug 19 '16 at 22:24
  • $\begingroup$ Why would it matter if it was spinning or not? What is a “fabring”? $\endgroup$ – JDługosz Aug 19 '16 at 22:43
  • $\begingroup$ @JDługosz Seems to me OP meant fabric. $\endgroup$ – a CVn Aug 21 '16 at 11:43
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Neutrons stars are extreme objects that measure between 10 and 20 km across. They have densities of 10^17 kg/m3 (the Earth has a density of around 5×10^3 kg/m3 )

A pebble 1 cm (0.01 m) radius, volume would be 4.188 x 10^-6, mass would be 4.188 x 10^11, That is 418800000 tonnes. And I don't think even 3 supermen could drag it.

Most of the space in an atom is empty, the electrons orbit really far away from nucleus. Neutron stars are made when atoms are disintegrated, into its fundamental components nucleus, and electrons which rather than orbiting zip around closely. It wouldnt be brittle (atleast I think so). If you make a weapon with it like a sword and somehow figure a way to use it, you don't have cut people, people will be attracted to it all you have to do it point it at them, they would be crushed by the gravity.

Making armours also wont work because things around would be attracted to it. You can make bullets for interstellar weapons and shooting at high speed at a planet, would wreck it.

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  • $\begingroup$ MCU Thor's hammer is made of that material. The only reason it doesn't end life on Earth as we know it is Odin's magic. $\endgroup$ – Renan Jul 21 '16 at 14:30
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    $\begingroup$ BTW I don't think that weapon would work by pointing. It would work by getting close to the target. I feel sorry for anyone appointed as the official wielder of that weapon XD $\endgroup$ – Renan Jul 21 '16 at 14:31
  • $\begingroup$ @Renan Yes; the gravitational attraction alone of a macroscopic object made from neutron star-like material would probably be enough to clear the battlefield. $\endgroup$ – a CVn Aug 21 '16 at 11:38
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    $\begingroup$ @Renan That's not actually true, his hammer was forged in a dying star but it's made of some fictional uru. $\endgroup$ – Vakus Drake Aug 21 '16 at 12:05
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Neutronium probably isn't the material that you want to use if you want to keep it even slightly plausible. It can't exist outside of a neutron star that has less than 2 solar masses squeezed into a 10 mile diameter. Anything less than that and the strong nuclear force would cause the outer layers to pop off, losing more mass, until it disintegrates into a cloud of neutron radiation.

But say you handwaved that part away.

Could you make armor out of it? No. It would be to heavy to move (like several earths heavy), and with so much gravity that anything in the vicinity around it would be pulled toward it, crushing down to a crusty patina on the surface.

Could you make a weapon out of it? Yes. Drop a chunk toward a planet and watch it shatter it's way through, and then the broken chunks would slowly form around the piece of neutronium.

Alternatives:

If you want an unbreakable armor, I'd personally suggest some super advanced alloy. Say they find a mysterious piece of metal, melt it down and combine it with other metals like iron to form something new.
Steel is an alloy of iron, carbon, and a few other metals depending on what properties you want it to have. By adding this mystery metal you could give it whatever properties you want.

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  • $\begingroup$ See this for supermaterials. $\endgroup$ – JDługosz Aug 19 '16 at 22:20
  • $\begingroup$ If you dropped a chunk of neutronium towards a planet, assuming it started at neutron star densities, the first thing it would do is rapidly expand/explode. Objects at those densities won't continue to exist once they're out of the neutron star or some other sort of crushingly high pressure containment vessel. $\endgroup$ – ckersch Aug 19 '16 at 22:21
  • $\begingroup$ @ckersch worse than that! Neutrons have a half-life of around 11 minutes… $\endgroup$ – JDługosz Aug 19 '16 at 22:25
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    $\begingroup$ @ckersch right, my answer does cover that, saying anything less than 2 solar masses would cause it to explode/disintegrate. But if you could keep it in its neutronium form through magic or whatever, it would destroy any planet it got close to, so wouldn't make good armor. $\endgroup$ – AndyD273 Aug 20 '16 at 1:31
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Yes it will still be super dense. I don't think the neutron star spinning has to do with the density, since the primary force is gravity. The density might factor into the strength, though it depends on what you want to measure. Hardness, tensile strength, shear strength, compressive strength, etc. is hard to be sure of, because it's so dense. Average mass exceed 500,000 earths, but average size is in the ballpark of 25 kilometers. Or a cubic centimeter of that stuff will weigh many hundreds of million tonnes. If you were dropped a meter above a neutron star, you'd likely accelerate to over seven million kilometers/hour. You get the picture.

But it also depends on what you're specifically asking for when you say the materials of a neutron star. The crust is likely iron atom cores and past that is simply a super-dense soup of neutrons. Beyond that you might get to a quark-gluon plasma, or a superfluid of neutron degenerate matter. Regardless, the theme here is extreme density. And thus, it would be extremely unlikely that you'd be able to move it, let alone work with it. You'd probably need some form of advanced gravitic manipulation, and even then it'd best be used not as armor but for something else.

We as a species don't understand them very well, but there's a reason dense materials do not necessarily make better armor. First there's the issue of weight, and workability. There are plenty of lightweight and very strong materials that are better suited to creating armor, especially for people. Even a starship's hull would likely be better with a lighter armor because of sheer mass and inertia. And as Chinu said, it would be extraordinarily efficient in kinetic bombardment again due to it's density, but said density is the primary limiter in its usefulness.

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  • $\begingroup$ The spin of a neutron star is not terribly important in its density. They do slowly spin down, since their magnetic fields tend to act as a brake, but as it slows, it will get very slightly denser, simply because "centripetal force" is getting weaker and thus opposing its gravity less effectively. $\endgroup$ – John Dallman Jul 21 '16 at 12:43
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Nothing.

Nothing will happen to the materials the neutron star is made of because their composition is in no way related to the spinning of the star, only its mass and radius. There would be a bit less centrifugal force counteracting the gravity near the equator, so there may be some minor changes in the equatorial crust, with some of the lighter nuclei in the crust clumping together to form heavier ones. The neutron star will remain a dense ball of neutronium with a thin crust of heavy, exotic atomic nuclei. It will be impossible to mine, because the gravity would kill you if you stepped foot on the surface.

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Your understanding of "neutron star material" is faulty. The reason neutron stars are so dense is because of their high gravity compressing that matter together, not some intrinsic property of the material itself. Basically a neutron star is what happens when a star's collapsed core isn't quite massive enough to become a black hole, but is fairly close.

So if you had a piece of neutron star material and took it out of the star's gravitational field, it would simply evaporate into free neutrons, which would soon decay into plain old hydrogen gas. If you removed it quickly, it would explode.

Now if you had an exotic material that had density comparable to that of a neutron star and was somehow stable... well, you'd certainly have some use for it, but it wouldn't make good armor because of its weight. If you had the energy to accelerate it or simply drop it from orbit, it would be an absurdly powerful weapon. As for how brittle it would be, that depends on its exact material properties, which are already nothing like that of a neutron star so you can make it whatever you want.

Also, it would make one heck of a paperweight.

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Let's go more with the scenario you are describing, than the question you start out by asking (which appears to be only peripherally related).

Let's assume that a "pebble" is approximately 1 cm3 in size.

Let's also assume that one of these adult men can carry somewhere on the order of 75 kg.

Let's also ignore how four men are able to simultaneously hold on to an object that is 1 cm3 in size, which is going to be a serious challenge, but not unsolvable, in itself.

With these assumptions, we can estimate the pebble's weight to be on the order of $4 \times 75~\text{kg} = 300~\text{kg}$.

As a consequence, the density of the material is something like $300 \times 10^6 = 3 \times 10^8$ kg/m3 (because $\frac{\text{cm}^3}{\text{m}^3} = 10^6$).

Apparently, osmium is the densest naturally occuring element on Earth, at 22.59 g/cm3 = $2.259 \times 10^4$ kg/m3. A pebble-sized ball of osmium would weigh a few tens of grams.

For back-of-the-envelope calculations, it's common to just look at the exponent. Your material is $10^{8-4} = 10^4$ times as dense as osmium. The actual result is that the material these men found is somewhere around 13,000 times as dense as osmium, but this figure could easily be anywhere from 10,000 to 15,000 times depending on how strong these men are.

For comparison, as pointed out by Chinu, a neutron star has a density on the order of $10^{17}$ kg/m3 (actually, several times that; Wikipedia states $3.7 \times 10^{17}$ to $5.9 \times 10^{17}$ kg/m3), which is another nine orders of magnitude (a billion times) more dense than the material you envision. A pebble-sized portion of a neutron star, assuming it stayed together (which it wouldn't, as IndigoFenix already pointed out), would weigh not 300 kg, but more like 300,000,000,000 ($3 \times 10^{11}$) kg.

In conclusion, basically and unfortunately, this question is another example of a lack of sense of scale in space.

I agree with AndyD273: It would probably be better, and less likely to risk loss of suspension of disbelief, to just have these men come up with a super-strong alloy instead. You don't even have to name or describe the parts to such an alloy unless you want to (but if you do, beware of falling into the same trap again by misestimating things).

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