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neilzero
2010-Feb-01, 03:27 AM
The consensus on previous threads seemed to be that 10 cubic kilometer of white dwarf stuff separated from a white dwarf would decompress back to ordinary matter. Much the same for a million cubic meters of neutron star stuff = neutronium.
If however the rather small compact mass was at the center of Earth's moon, would the pressure be sufficient to prevent or greatly slow the decompression of the compact matter? Assuming that either arrangement is viable long term, what would be the new surface gravity of Earth's moon? Neil

WaxRubiks
2010-Feb-01, 05:02 AM
I would think it would blow up the moon, myself, if the neutron matter were to return to the density of ordinary moon matter.

korjik
2010-Feb-01, 05:21 AM
10^6 m^3 of matter at 4*10^17 kg/m^3 would make the Moon about 6 times more massive. Surface gravity at the same radius would be about the same as the Earth.

Since it takes about 10^31 kg to get a mass large enough to make a neutron star in the first place, I cant see the 10^22 kg of the moon doing anything to the block of neutronium. How much bang you get for that much neutronium is anyones guess tho

trinitree88
2010-Feb-01, 05:04 PM
The consensus on previous threads seemed to be that 10 cubic kilometer of white dwarf stuff separated from a white dwarf would decompress back to ordinary matter. Much the same for a million cubic meters of neutron star stuff = neutronium.
If however the rather small compact mass was at the center of Earth's moon, would the pressure be sufficient to prevent or greatly slow the decompression of the compact matter? Assuming that either arrangement is viable long term, what would be the new surface gravity of Earth's moon? Neil

neilzero. The binding released when small nuclei fuse to larger ones, must be returned to unbind the dwarf stuff, not to mention the gravitational potential energy, which also must be returned. This is not trivial.

neilzero
2010-Feb-01, 06:05 PM
Hi Frog March: Some thickness of ordinary matter should provide enough pressure to prevent the small nuclei from reverting to large nuclei. How about 1/10th solar mass of ordinary matter at an average density of 100? Is that about the average density of a brown dwarf? Is the answer lots different for neutron star stuff?
I agree, if it starts rapid expansion, even a brown dwarf will be blown apart by the expansion. Do we get banished to ATM = against the mainstream if we hint at exploding planets? Seriously I have no idea how the white star stuff could be placed at the mass center of anything with less mass than a white dwarf. It is a thought experiment. If korjik is correct, it is a great way to terraform the moon, assuming the puny 10^22 kg provides enough pressure to keep the nuclei small. Diamonds don't explode in a vacuum, and the surface of the white dwarf does not explode even though the pressure is much less than at the mass center of the white dwarf. There must be some hysteresis. Do white dwarfs have a thick crust of ordinary matter. Sorry, each analysis suggests more questions. Neil

korjik
2010-Feb-01, 07:35 PM
Hi Frog March: Some thickness of ordinary matter should provide enough pressure to prevent the small nuclei from reverting to large nuclei. How about 1/10th solar mass of ordinary matter at an average density of 100? Is that about the average density of a brown dwarf? Is the answer lots different for neutron star stuff?
I agree, if it starts rapid expansion, even a brown dwarf will be blown apart by the expansion. Do we get banished to ATM = against the mainstream if we hint at exploding planets? Seriously I have no idea how the white star stuff could be placed at the mass center of anything with less mass than a white dwarf. It is a thought experiment. If korjik is correct, it is a great way to terraform the moon, assuming the puny 10^22 kg provides enough pressure to keep the nuclei small. Diamonds don't explode in a vacuum, and the surface of the white dwarf does not explode even though the pressure is much less than at the mass center of the white dwarf. There must be some hysteresis. Do white dwarfs have a thick crust of ordinary matter. Sorry, each analysis suggests more questions. Neil

I meant cant see the moon affecting the neutronium. Normal matter is a pretty good vaccum to neutronium. Even matter that is 10^5 kg/m^3 is still 12 orders of magnitude less dense than the neutronium.

Without some outside means of containment, the neutronium would decay as you pulled it off of the neutron star. If you have the containment, then you have a way to increase masses.

BigDon
2010-Feb-01, 09:01 PM
neilzero. The binding released when small nuclei fuse to larger ones, must be returned to unbind the dwarf stuff, not to mention the gravitational potential energy, which also must be returned. This is not trivial.

I don't think they heard you Trin.

BigDon
2010-Feb-01, 09:18 PM
Darn, I hit submit by mistake.

We're not talking about mere modulus of compression here.

(I presume there isn't a mathematically significant deference, once you have the pressure to do so, to covert a given volumne of lithium, iron or mercury into neutronium)

Once you have the neutronium, what would be the source of internal tension for it to re-expand spontaniously into non-neutronium?

korjik
2010-Feb-01, 09:23 PM
The source of energy is the decay of neutrons into protons and electrons.

The binding energy that allowed the neutronium to form would have been gravitational. Once you pulled the neutronium out of the neutron star, you removed most of that binding energy.

korjik
2010-Feb-01, 09:27 PM
neilzero. The binding released when small nuclei fuse to larger ones, must be returned to unbind the dwarf stuff, not to mention the gravitational potential energy, which also must be returned. This is not trivial.

You have a 10^23 kg atomic nucleus. It is about 10^48 times as massive as a Uranium atom. Do you think it might be a little radioactive?

Energy is also released when larger atoms decay. Neutronium is even worse than standard atoms.

Philippe Lemay
2010-Feb-02, 03:55 AM
*thinks*

Oh this idea is just cool! Even if the scientific realism is questionable, this would be an awesome way for advanced races to terraform small moons in sci-fi stories.

Points to you for coming up with the idea man.

eburacum45
2010-Feb-02, 04:42 AM
From wiki

While bound neutrons in stable nuclei are stable, free neutrons are unstable; they undergo beta decay with a mean lifetime of just under 15 minutes (885.7 ± 0.8 s). A lump of neutronium suddenly released from the pressure that holds it stable would be very, very radioactive, turning into a gas of protons and electrons within minutes.

If you want to make a Moon-sized object with Earth-like gravity, don't use a neutron star, use a black hole, which would be stable at any mass greater than a small asteroid.

Step 1: create an artificial black hole with a mass 6 times as massive as the Moon. It would be stable for the foreseeable future, and a tenth of a millimetre in radius.
Step 2: place a shell around that hole at the radius of the Moon. This would give you a surface gravity of 1 gee.
Step 3. Add atmosphere and live there.

Of course you have to stop the shell from falling into the hole, but there are ways to do that (at least in theory).

Philippe Lemay
2010-Feb-02, 04:59 AM
I suppose, but neutronium-tech sounds less outlandish than black-hole-tech.

To me it does anyway.. though I guess when you get right down to it they're both equally far out there.

Dragonchild
2010-Feb-02, 05:07 AM
I meant cant see the moon affecting the neutronium. Normal matter is a pretty good vaccum to neutronium. Even matter that is 10^5 kg/m^3 is still 12 orders of magnitude less dense than the neutronium.

Some of the neutronium would quickly decay into free hydrogen gas. Starting with a mass 6x that of the Moon itself, even in the first few seconds and a gas as diffuse as hydrogen plasma we're talking about an awful lot of angry electrostatic pressure. Wouldn't the formation of that gas and the resulting electrostatic repulsion create a massive shockwave that annihilates the Moon?

Either I'm crazy, or that'd be one helluva bang.

WayneFrancis
2010-Feb-02, 08:24 AM
I suppose, but neutronium-tech sounds less outlandish than black-hole-tech.

To me it does anyway.. though I guess when you get right down to it they're both equally far out there.

I think they both have major problems.

Neutronium is highly unstable without the gravitational energy of the actual neutron star.

Black hole...well how hot would it be from hawking radiation? How hard would it be to build shell around it.

Be a lot easier to bring together normal matter with the mass of the Earth and live on it....

Honestly neither is ever going to happen. Might as well talk about building a city made entirely of silly puddy.

To the OP...you got your answer....Pressure from normal matter will not help keep the material from changing.

eburacum45
2010-Feb-02, 01:30 PM
how hot would it be from hawking radiation? A black hole six times as massive as the Moon would be cooler than the Cosmic background radiation.

How hard would it be to build shell around it. Not perhaps impossible, if you use dynamically supported orbital rings.
http://en.wikipedia.org/wiki/Orbital_ring

I've written a fiction page about various ways of making artificial planets to order; it is a big task, and there are real difficulties, but neutronium is not really usable in this context (too unstable).
http://www.orionsarm.com/eg-article/49a3ee435bd98

WayneFrancis
2010-Feb-02, 03:50 PM
A black hole six times as massive as the Moon would be cooler than the Cosmic background radiation.
...

I just did the maths...~1.7K. I should have just done that.

As for the rest I still stand by the fact that there are much easier ways to make something to live on then building a shell around a black hole.

eburacum45
2010-Feb-02, 09:46 PM
As for the rest I still stand by the fact that there are much easier ways to make something to live on then building a shell around a black hole. Well, that is true. To get gravity all you need to do is make a hollow cylinder or sphere and spin it; if you can prevent it from tumbling you have centrifugal force which will replicate gravity.

The biggest design for a rotating cylinder I've seen is that proposed by Tom McKendree of NASA; a cylinder reinforced with carbon nanotube could be about 2000km in diameter and 10,000km long. More living space than the Moon and much lower tech than a black hole suprashell.

neilzero
2010-Feb-02, 11:22 PM
Hi trim: Do I understand unbind and return as BigDon seems to infer that even one gram samples of neutronium and white star stuff would need to absorb large amounts of energy to revert to ordinary matter = very stable? My first thought was that small nuclei is the compressed matter, but BigDon seems to imply that large nuclei is the white dwarf star stuff or neutronium? Please clarify. A gram of white star stuff would have dimensions of a few plank lengths and one gram of neutronium would be about 1/10th those dimensions. Perhaps bits of white dwarf star stuff and neutronium are common in our biosphere, but much too small to detect? Perhaps nebula clump around such bits to form asteroids, comets, planets, moons, and suns? Compact matter seeds rain fall? Neil

neilzero
2010-Feb-03, 12:27 AM
Korjik asked do you think it might be radioactive? Perhaps in near vacuum, or even near the mass center of a neutron star, but it is comparing elephants to oranges. Ordinary nuclei are made of protons, neutrons and some other subatomic particles White dwarf star stuff has extra electrons in the nucleus plus protons, nuetrons and other sub atomic particles. Neutronium is mostly neutrons. Quarkstar stuff is mostly quarks and electrons, I think. Over simplified = likely. How about one kilogram of quark star stuff? Neil

korjik
2010-Feb-03, 08:26 PM
Some of the neutronium would quickly decay into free hydrogen gas. Starting with a mass 6x that of the Moon itself, even in the first few seconds and a gas as diffuse as hydrogen plasma we're talking about an awful lot of angry electrostatic pressure. Wouldn't the formation of that gas and the resulting electrostatic repulsion create a massive shockwave that annihilates the Moon?

Either I'm crazy, or that'd be one helluva bang.

Plasma is (mostly) electrically neutral. No electrostatic force.

korjik
2010-Feb-03, 08:29 PM
I just did the maths...~1.7K. I should have just done that.

As for the rest I still stand by the fact that there are much easier ways to make something to live on then building a shell around a black hole.

Did you check how long it would last?

Grey
2010-Feb-03, 08:40 PM
Did you check how long it would last?I like this (http://xaonon.dyndns.org/hawking/) website, which does all your Hawking radiation calculations at once. It's excellent for the lazy. :) A black hole with that mass will last much, much longer than the current age of the universe, so no worries about it evaporating out from under you.

IsaacKuo
2010-Feb-03, 08:48 PM
A lump of neutron star matter placed in the center of the moon isn't going to take "minutes" to turn into something else. It's going to instantly explode due to neutron degeneracy pressure. That former lump of matter will be thoroughly mixed with the surrounding (now also exploding) lunar material long before you have to worry about radioactivity or free neutron decay.

There's also the matter of perhaps a million degrees worth of kinetic energy, but that's peanuts compared to the neutron degeneracy pressure--if it were up to temperature pressure alone, then the neutron star would have collapsed into a black hole.

WayneFrancis
2010-Feb-04, 03:11 PM
Did you check how long it would last?

if I did it right its on the order of 1x1045 years

So a very long time.

korjik
2010-Feb-04, 05:33 PM
if I did it right its on the order of 1x1045 years

So a very long time.

Yeah, I saw that on the site Grey linked to. My WAG was only off by about 40 orders of magnitude. :)

Philippe Lemay
2010-Feb-19, 07:51 PM
(Thought of this today at work) What if we don't use neutronium, and only take regular matter.

We know natural matter can reach at least 20 tons/m³, through super dense metals. So what if we just injected matter into the moon's mantle? We're already suggesting moving 5 lunar masses into Luna's core, what if instead of manipulating it into neutronium we just heat it into a plasma state. We could then channel the plasma-ed rock using powerful magnetic fields and guide it into deep shafts dug into the moon's crust.

For the original matter we could use large asteroids that were nudged into cis-lunar orbit. And to super heat them into plasma maybe we could use a massive solar array, or some kind of fusion power (or a little bit of both).

I just wonder... would pumping too much new matter into the moon's mantle and core cause strain on the crust? Ideally we would want to keep the same diameter and only increase the mass. But I imagine we might have to deal with a few... moon-quakes, maybe even some chasms that would open up.

But, assuming that the pressure holds, we keep the magnetic fields running until the plasma cools and the shaft openings re-solidify. Then we wait for the surface to cool down sufficiently for humans to set foot on it. The advantage of this approach is that we know how to turn regular matter into ionized plasma (usually just by heating it), but we don't yet know how to turn matter into neutronium. It would still be astronomically difficult, probably taking thousands of years. But hey, this is terraforming.

I'm even wondering... maybe we could inject the new matter in such a way to cause the moon's core to spin. Maybe give the moon it's own little magnetic field? Or would that be pushing my luck?

BigDon
2010-Feb-20, 02:31 AM
*thinks*

Oh this idea is just cool! Even if the scientific realism is questionable, this would be an awesome way for advanced races to terraform small moons in sci-fi stories.

Points to you for coming up with the idea man.

"Genesis device? You mean Genesis Torpedo!"

So what's the ball park yield on a cubic decimeter of fissioning, if that's the right term, neutronium?

(Stick with me Philippe, no seven foot tall blue monkeys will stop us!)

Philippe Lemay
2010-Feb-20, 04:29 AM
?... excuse me?

I have no idea what the yield of of neutronium is, Neilzero and eburacum seem to have much more experience crunching those numbers than I do. If you had bothered to read my latest post, you would have seen that I am suggesting an ALTERNATIVE to using neutronium. A substance that, for all we know, we may never master.

I also don't understand what connection you saw between my posts and Star Trek or Avatar (not too subtle a hint with the tall blue monkeys there...) Star Trek used a "Genesis Device" to terraform an arid planet's surface. So far as I know (I've never actually seen the whole movie, not really a fan of Trek), the planetoid in question was not a moon, and they didn't mess with it's core, just the surface.

So... yea, I really don't know what you're going on about. But I take serious offense to being called a "Star Trek nerd", I've always been very disappointed with Star Trek's lack of realism and repetitive storyline. I'm not saying it's bad sci-fi, I'm just saying I'm not a fan. But I'm side-stepping the issue here. The subject we are debating is how best to terraform a moon by increasing it's surface gravity.

korjik
2010-Feb-20, 07:08 AM

"Genesis device? You mean Genesis Torpedo!"

So what's the ball park yield on a cubic decimeter of fissioning, if that's the right term, neutronium?

(Stick with me Philippe, no seven foot tall blue monkeys will stop us!)

If I have my numbers right: 7 trillion megatonnes in released energy

NorthernBoy
2010-Feb-20, 09:01 AM
You have a 10^23 kg atomic nucleus. It is about 10^48 times as massive as a Uranium atom. Do you think it might be a little radioactive?

Energy is also released when larger atoms decay. Neutronium is even worse than standard atoms.

This is a good way to put it, I think. Talking about the binding energy as keeping the mass in the form of Neutrons makes no sense at all, neutrons are unstable in most arrangements, and you need a huge amount of gravity to shift them to being stable.

BigDon
2010-Feb-20, 01:27 PM
?... excuse me?

I have no idea what the yield of of neutronium is, Neilzero and eburacum seem to have much more experience crunching those numbers than I do. If you had bothered to read my latest post, you would have seen that I am suggesting an ALTERNATIVE to using neutronium. A substance that, for all we know, we may never master.

I also don't understand what connection you saw between my posts and Star Trek or Avatar (not too subtle a hint with the tall blue monkeys there...) Star Trek used a "Genesis Device" to terraform an arid planet's surface. So far as I know (I've never actually seen the whole movie, not really a fan of Trek), the planetoid in question was not a moon, and they didn't mess with it's core, just the surface.

So... yea, I really don't know what you're going on about. But I take serious offense to being called a "Star Trek nerd", I've always been very disappointed with Star Trek's lack of realism and repetitive storyline. I'm not saying it's bad sci-fi, I'm just saying I'm not a fan. But I'm side-stepping the issue here. The subject we are debating is how best to terraform a moon by increasing it's surface gravity.

A mis-communication my good sir.

Had I written that better I would have indicated that *I* was the Star Trek nerd, as I was the one who was using Star Trek quotes. I apologize for that.

I was trying to point out that much like that Klingon captain, tool or weapon is in the eye of the beholder.

Who's moon are we talking about, ours? Shoot, just gas it up with an atmosphere. If you just gave the Moon a sea level atmosphere it would take on the order of 3000 years to bleed off to levels lower than you could breathe. Mars would take ten thousand years.

I would even mess with the neutronium because think about it, if you could harvest it you wouldn't need it! A neutron star is the second deepest hole they make. You would need the power of a singularity to mess with it.

Philippe Lemay
2010-Feb-20, 05:15 PM
Ok, sorry if I over-reacted.

Star Trek is a somewhat sensitive issue with me, and terraforming a planet in like... what was it, 3 minutes in the movie? .. is an inexcusable leap in the realism of sci-fi. ANYWAY, let's leave this uncomfortable little misunderstanding aside.

I think this thought experiment is mainly aimed at our own Luna, yes. But the same technique could be used with many of the other moonlets and planetoids in our system. As I'm sure you all know, Earth is the planet with the highest surface gravity (ignoring the gas giants for a second). This means that even if we terraform Mars and Mercury and the Moon, and the Moons of Jupiter in virtually every other way: Atmospheric pressure, water, top soil and compatible plant life, human colonists would still have to deal with bone degeneration in the long term. Which is why I consider increasing the surface gravity to be an important part of terraforming.

Another interesting concept to minimize the negative effects of low gravity on the human body is to somehow genetically engineer humans so that they're bones can still grow strong without heavy gravity. I'm not sure exactly how this could be done, so it's still entirely theoretical. But it could make a long term presence on the Moon or Mars easier than if we just used 100% natural human colonists.

loglo
2010-Feb-22, 04:07 AM
*thinks*

Oh this idea is just cool! Even if the scientific realism is questionable, this would be an awesome way for advanced races to terraform small moons in sci-fi stories.

Points to you for coming up with the idea man.

Will McCarthy's "The Collapsium" explored those themes. He used black hole stabilised neutronium balls as a building block.

I'm also reminded of the little spacecraft used by the Cheela in Forward's Dragon Egg. They were also black hole stabilised neutronium of some kind.

neilzero
2012-Aug-08, 06:22 PM
How about a non-rotating Moon size sphere of metal averaging 20 times the density of water, with ten kilometer of Earth like soil on the outside. How thick (800 miles, perhaps) does the metal shell have to be to get one g outer surface gravity? The interior could be near vacuum helium which would add very little mass. I understand all the interior would be close to zero g. I suppose adding a one bar atmosphere at the center of mass would affect the outer surface gravity only slightly, but a significant atmosphere inside would increase the outer surface gravity by several percent? Would 800 mile thick platimum be strong enough to survive a small million ton asteroid hit with vacuum inside? Neil

Grey
2012-Aug-08, 07:15 PM
Still thinking about this, hmm? Looking here (http://www.transhuman.talktalk.net/iw/Geosync.htm), having 0.075 Earth masses at 20 g/cm3 gets you 1 g, while being just about the size of Luna. So you'd have a solid sphere, not a hollow one (which is good, because a hollow sphere that massive would collapse on itself). That density is about twice what it would be if it were solid iron, so as you suggest, you'd have to pick some of the much denser metals to be able to build this. If you've got that much platinum, though, you could definitely do this without worrying about containment technology for neutronium.

neilzero
2012-Dec-25, 07:25 AM
If we have a material a million times a million times stronger than steel we can make three concentric spheres each with a radius of about one million kilometers, and one centimeter thick. The inner sphere is filled with vacuum so it adds negligible mass. The surface area of the middle sphere is 12.56 times 10*12 = 12,560,000,000,000 square kilometers, which can be home to at least a million times the present population of Earth. Problems are very little gravity, no source of energy, food, water, or other supplies. The volume of material needed for the 3 spheres is three times 10*16 cubic centimeters = 3 times 10*10 cubic meters = 30,000,000,000 cubic meters = perhaps 100,000,000,000 tons of material plus a breathable atmosphere for the people who live between the outer and the middle spheres perhaps 3 meters head room. Ducts etc can be in the vacuum between the middle sphere and the inner sphere except rare locations where 6 meters of head room or a habitable basement are desired. Neil

neilzero
2012-Dec-25, 07:28 AM
When gas expands, it gets cold, but about half the posts seem to be saying a few billion degrees k when neutonium expands. Should I assume a few milion k when white star stuff expands? Same for quark star stuff, if there are any quark stars?
Possibly Philip's procedure can give the moon a core and mantal of Osmium with a radius of 1000 kilometers, or the osmium can be obtained and installed near the center of our moon by some other method. That would give our moon more gravity than the surface of Mars, possibly as much as Earth's gravity, even though the moon's radius would be increased by perhaps 50%, especially if the osmium was very hot. Tungstan, platimum, gold, and Uranium are almost as dense as osmium, and likely all would increase in density at least slightly due to the much higher than standard pressure. Neil

publiusr
2012-Dec-28, 11:14 PM
That would be something to see. This might be as good as it gets