Neutron Stars: Total Compaction?

[Jim Leff]

Is all space between electrons, protons, and neutrons completely eliminated in a neutron star? I'm not sure if there is ordinarily space between quarks, but, if so, are they also completely compacted?

I guess the basic question is, how much space, at whatever level, remains within neutron start material?

[Ann]

In a recent thread (and I'm afraid I don't remember which one) someone (Bruce Daniel Mayfield?) pointed out that since pulsars are believed to be neutron stars, and since they are highly magnetic, they can't be made entirely of neutrons. Neutrons are electrically neutral, and can't generate an electric current or magnetism.

So I agree with Bruce(?) that neutrons stars can't be totally compacted. If nothing else, they must have a supply of electrons.

Ann

[Chris Peterson]

Is all space between electrons, protons, and neutrons completely eliminated in a neutron star? I'm not sure if there is ordinarily space between quarks, but, if so, are they also completely compacted?

I guess the basic question is, how much space, at whatever level, remains within neutron start material?

Neutron stars vary in composition with depth below their surface. The outer layer is iron (which is why such stars have magnetic fields). Different elements are present below the surface, until the pressure becomes so high that you end up with a degenerate neutron fluid. A neutron doesn't have a size in the classical sense, so it's a bit meaningless to talk about the space between neutrons that isn't part of those same neutrons. But the spacing between neutrons depends on density, which increases deeper in the star.

[Nitpicker]

The reality of "space" is different at the quantum scale, which is a deliberately vague statement, but one which makes sense to me. How long is a piece of string?

[Jim Leff]

Thanks, guys. I'm not getting quite the answer I'm looking for, so I'm clearly not asking the right question!

Anyone who observes sub-atomic particles, the immediate environment, and the inconceivably vast spacing between stars, galaxies and galactic groups has to marvel at the realization that the universe is, at every level of scale, almost entirely nothing. The Hindus call it "akasha" - the apparent emptiness underpinning apparent solidity.

I once heard a scientist explain the marvel of the big bang by noting that everything's mostly nothing, anyway, so the original compaction wasn't all THAT unimaginable.

Aside from the singularity of black holes, and disregarding mathematical models of what's actually physically possible, compaction-wise, is neutron star material still, at any level, still rife with space?

So I'm asking a pretty simple question. It may not have an answer. But hopefully this more fleshed-out posting will illustrate that I'm not asking out of an interest in distinction-drawing or the fine points of neutron stars, per se. If you hypothetically (I'm not interested in real-world possibilities) compress matter to the point where there's no space left, would that have the density of neutron stars, or would it be extremely more dense still?

[Nitpicker]

I'm going to make an educated guess that some neutron stars are denser than others, and the density increases as you go deeper within all of them. Purely based on that, it would seem that they would all be theoretically compressible, or capable of having their density increased by some means. But talk of "space versus matter" is above my pay scale.

[Ann]

Jim Leff wrote:
Aside from the singularity of black holes, and disregarding mathematical models of what's actually physically possible, compaction-wise, is neutron star material still, at any level, still rife with space?

The way I understand it, yes, absolutely. Neutrons themselves are "rife with space" (I love that expression), so if neutron stars are made of neutrons, they must be rife with space.

Could a neutron star contain a black hole in its center? What an interesting question. If it does, the black hole must start eating away at the neutrons surrounding it. I believe that if the black hole is extremely small, it can't eat fast at all, so it would take a considerable time for it to eat much of the neutron star.

Could the mini black hole eat with good table manners, though? Wouldn't it create such a mess in the neutron material surrounding it that you could tell from the outside that the neutron star was having indigestion?

Or maybe the incredibly compact neutron star material would stop any "jets" or accretion disks from forming, let alone making it outside the neutron star so that observers could see them from outside?

Ann

[Chris Peterson]

Could a neutron star contain a black hole in its center?

No. Not unless it came from an external source. A neutron star is a neutron star, and not a black hole, because it isn't massive enough to overcome neutron degeneracy pressure.

[Jim Leff]

Neutrons themselves are "rife with space", so if neutron stars are made of neutrons, they must be rife with space.

Thanks.

So if you compressed the neutrons completely in the densest sort of neutron star material (a spoonful containing the mass equivalent of Everest), what would be the density of the result (in a similar real-world analogy)? I'd imagine it's a reasonably straightforward matter of gauging the mass and volume of the constituent quarks. If I had the math training, I'd do it myself.

[geckzilla]

I think the answer you need is "Nobody knows" because nobody knows. I doubt it's the answer you want, though.

[Nitpicker]

So if you compressed the neutrons completely in the densest sort of neutron star material (a spoonful containing the mass equivalent of Everest), what would be the density of the result (in a similar real-world analogy)?

The density would be the mass of Everest divided by the volume of a spoonful. You asked.

[Jim Leff]

So if you compressed the neutrons completely in the densest sort of neutron star material (a spoonful containing the mass equivalent of Everest), what would be the density of the result (in a similar real-world analogy)?

The density would be the mass of Everest divided by the volume of a spoonful. You asked.

Thanks, but you answered a question I actually didn't ask!

[Nitpicker]

My apologies. I read the densest sort to be the densest sort.

[Jim Leff]

My apologies. I read the densest sort to be the densest sort.

By densest sort I meant densest sort. But the point is we're then DOING something to this material (hypothetically).

[Ann]

My apologies. I read the densest sort to be the densest sort.

By densest sort I meant densest sort. But the point is we're then DOING something to this material (hypothetically).

It is my amateur understanding that neutrons will remain rife with space until gravity overwhelms that which keeps the neutrons from collapsing (which may be called the Pauli exclusion principle or something). So if gravity suddenly gets the upper hand, a neutron star will just suddenly change from being a neutron star and turn into a black hole. This would happen if the neutron star was to collide with another neutron star, for example (or so I think).

Ann

[owlice]

Jeff, the wikipedia page on neutron stars is pretty good (http://en.wikipedia.org/wiki/Neutron_star) and of course also provides other sources of information. You might like Dr.Miller's page on neutron stars (from the University of Maryland Astronomy Department, or this page from Space.com as well.

[THX1138]

The whole mess is so confusing to me. Some stars burn till there is noting but carbon left, one big giant diamond? Some end their lives when the start creating iron and so go supernova? Some collapse into neutron stars, black holes, pulsars…………The list seems endless

[Jim Leff]

I'm so sorry to be such a pain....I don't often have such trouble expressing myself clearly. I'm not asking "how dense is a neutron star?" Nor am I asking "how dense can a neutron star be?"

My original question was whether the density of a neutron star is absolute. The answer (courtesy of Ann) is, apparently, "no", because quarks are mostly space. So there's more hypothetical compaction to be achieved. So the question has turned to: how dense would be the result if we (hypothetically) compressed all the space out of the quarks in a material that's otherwise as dense as can be? I.e. what's the density when all space is gone? It's not a ditzy question. It's an interesting and profound one. And the answer would be simple for anyone with some math skills IF the volume of space in a quark is known. If not, then it's unanswerable. I understand that quantum issues bend the issue at this scale, but perhaps there's a way around that to get to the gist of what I'm asking.

[Chris Peterson]

I'm so sorry to be such a pain....I don't often have such trouble expressing myself clearly. I'm not asking "how dense is a neutron star?" Nor am I asking "how dense can a neutron star be?"

My original question was whether the density of a neutron star is absolute. The answer (courtesy of Ann) is, apparently, "no", because quarks are mostly space. So there's more hypothetical compaction to be achieved. So the question has turned to: how dense would be the result if we (hypothetically) compressed all the space out of the quarks in a material that's otherwise as dense as can be? I.e. what's the density when all space is gone? It's not a ditzy question. It's an interesting and profound one. And the answer would be simple for anyone with some math skills IF the volume of space in a quark is known. If not, then it's unanswerable. I understand that quantum issues bend the issue at this scale, but perhaps there's a way around that to get to the gist of what I'm asking.

The problem with your question is that it doesn't define "space" or "empty space". There is probably no such thing as matter packed together with no space, for the simple reason that there's probably no such thing as solid matter at all when you get small. There is only space. The "size" of subatomic particles is only a reference to the size and shape of the fields that those particles create. The particles themselves are not solid in any classical sense.

Density makes sense. The ratio of solid to space really doesn't.

[rstevenson]

The whole mess is so confusing to me. Some stars burn till there is noting but carbon left, one big giant diamond? Some end their lives when the start creating iron and so go supernova? Some collapse into neutron stars, black holes, pulsars…………The list seems endless

No stars burn until there's nothing but carbon left. That size of star stops burning when it reaches carbon, but only because it isn't massive enough to compress the core down into a hotter ball to burn what's left in the core. There's lots of hydrogen in the star at that point, but it's out in the shell of the star where it's too cool to burn.

Any star large enough to create iron stops at that point. No star can be more massive than that, so iron is the top (bottom?) of the food chain for stars. Then, Kaboom!

Just think of the whole burning, stopping, and perhaps exploding chain of events as based entirely on mass -- less massive stars do one thing, medium mass stars another, large mass stars yet another. The Stellar evolution page at Wikipedia has a good explanation of the process.

Rob

[Jim Leff]

The problem with your question is that it doesn't define "space" or "empty space". There is probably no such thing as matter packed together with no space, for the simple reason that there's probably no such thing as solid matter at all when you get small. There is only space.

So it's not that the universe is mostly nothing, it's that it's truly nothing? Wow, that's pretty incredibly interesting. I'm imagining you quibbling with my terminology in framing it that way, but rereading your phrase "there is only space", it strikes me as damned clear!

But, backing up a little....you say "there is probably no such thing as matter packed together with no space". Will you accept that matter can, at least hypothetically/theoretically, be packed much denser than in the densest neutron star? If so, how dense can it go before you start to get exasperated with the question? Preferably expressed in real world volume terms (ala tablespoon everest). And if this isn't your field (we're obviously far from astrophysics here!), no problem, I'll pursue the issue elsewhere and thank you for your very interesting input!

[rstevenson]

But, backing up a little....you say "there is probably no such thing as matter packed together with no space". Will you accept that matter can, at least hypothetically/theoretically, be packed much denser than in the densest neutron star?

Hi Jim. May I interject?

There exists, in a sense, exactly what you're asking about, a substance with no space between particles. Here, from the Wikipedia article on Black Holes, is the relevant paragraph...

At the center of a black hole as described by general relativity lies a gravitational singularity, a region where the spacetime curvature becomes infinite. For a non-rotating black hole, this region takes the shape of a single point and for a rotating black hole, it is smeared out to form a ring singularity lying in the plane of rotation. In both cases, the singular region has zero volume. It can also be shown that the singular region contains all the mass of the black hole solution. The singular region can thus be thought of as having infinite density.

So when you put all the mass of the star that became the black hole, plus any mass it's accumulated since, into a region of zero volume, you get infinite density. If that doesn't qualify as no space between particles, I don't know what does. But it also means no particles (remember that bit about zero volume), so our conclusion must be that there will be space between particles all the way down to the black hole state, and then you have neither particles nor space. (But don't ask me where the BH's gravity is coming from if all its mass is in a region of zero volume.)

Hope that clarifies a bit.

Rob (I'm not a physicist but I stayed at a Holiday Inn last night)

[Jim Leff]

Thanks, Rob. I was hoping not to get into black holes in this discussion, since they're such a distinct and inexplicable case.

I'm talking about the densest imaginable theoretical/hypothetical compaction of matter up to but not including singularity and all that weirdness.

(but don't think I didn't grok the singularity implications of Chris' "there is only space" remark, or that once I find what I'm looking for that I won't be brooding about black holes, big bang, and the rest of the cosmological rabbit hole!).

[Chris Peterson]

Will you accept that matter can, at least hypothetically/theoretically, be packed much denser than in the densest neutron star?

The matter in a neutron star is supported by neutron degeneracy pressure. You can increase the pressure by adding mass, which will increase the density (where density refers to the number of neutrons in some volume, not the ratio of neutron to space). But you can't increase the density by much, because once you exceed the maximum force that neutron degeneracy pressure can provide, you collapse into a black hole. Now, if you want to consider the center of a black hole to be a physical singularity, then you have something with infinite density. Or it might be some sort of exotic matter, with extremely high density. Or it might be nothing at all, in the sense that a black hole may have no interior, but is more like a fundamental particle. Nobody really knows. But outside of some fairly exotic theory (like quark stars), the matter at the center of a neutron star is probably as dense as matter can get while it's still matter as we generally understand the term.

[Ron-Astro Pharmacist]

Space seems to be the one intangible aspect of our physical experience we have trouble understanding. Quantum theory (the little I understand) depicts it to contain short-lived particles. Since we haven’t found dark matter, as far as I know, I frequently am curious if it is part of the emptiness also. And is the space outside the atom the same as the space between the nucleus and its electrons; provided they are not ionized? I can’t seem to eliminate the possibility that, if that space had the capability to hold dark matter, is light simply a composite wave/particle of dark matter with its angular momentum? After all isn’t most of an atom’s space in the area where the electron roams? With light causing electrons to move to and from their various levels, couldn’t this be the reflection of a loss or a gain of a dark matter particle/wave with a spin (light)? Of course that would make one curious as to what is the mixture of dark matter the opposite angular momentum.

A figment of my imagination?? Probably but its fun thinking about it!!