In neutron stars, astrophysicists see a form of matter like none other
nautil.us
nautil.us
The article mentions the equation of state. Fun fact: neutron stars are probably the most complex objects in the Universe. Black holes by comparison are quite simple: describle with three quantities (mass, spin, electric charge). An equation of state would tell us how large these can get, for example.
Consider the nucleus of a normal atom. We know and have mapped out electron shell structures. Nuclei too have structure but it's way more inscrutable and complex as you have to deal with the electric repulsion between protons, the strong interaction between quarks (and gluons) and the strong interaction between nucleons. AFAIK we don't really have a good model for this.
Now imagine that scaled up to something 20km across where gravity has also become a significant force and obviously we don't have a quantum model for gravity anyway.
In addition to all of that you have to deal with fluid dynamics. The article mentions nuclear pasta and theorized crystalline structure within a neutron star but in outer layers its likely it acts more like a fluid.
And then there's things can collide in unbelievable energetic interactions, such that we can detect the ripples in space-time billions of light years away. We're talking 5-10 Solar masses converted to energy in less than a second.
[1]: https://en.wikipedia.org/wiki/Magnetar
EDIT: fixed Solar mass typo
> Black holes by comparison are quite simple: describle with three quantities (mass, spin, electric charge).
For an actual black hole (vs. theoretical-in-a-vaccuum one), I believe 2 other number are required - to specify which way the spin axis points. [EDIT - still not right. 11 numbers are needed to cover everything; see my Wikipedia cite below.]
> We're talking 50-10 Solar masses converted to energy...
Obvious "50-10" typo. But beyond ~6 Solar masses total, at least one of the two object will have long-ago collapsed into a black hole.
Plus you can just "rotate" a black hole to get it to have the same spin axis as another black hole. You can't "rotate" or "translate" a black hole in space to make the other three numbers change. Those require ingesting matter or emitting hawking radiation and that is the only thing that changes those properties.
> Plus you can just "rotate" a black hole to get it to have the same spin axis as...
Quip: If you have the tech & budget to meaningfully rotate a spinning black hole, then you've got the tech & budget to change the other parameters, too.
FWIW - Wikipedia's answer is that 11 numbers (or 2 scalars and 3 vectors) are needed to fully spec. a stable black hole - https://en.wikipedia.org/wiki/Rotating_black_hole#Types_of_b...
Two black holes who differ only by their position, linear and/or angular momentum but are equal in all other parameters are not distinguishable from simply seeing the same black hole twice from a different perspective.
Two black holes who differ in any of the three properties of mass, spin or magnetic charge are distinguishable by those properties (but even that is arguable to some extend).
edit: The rent prices of a planet don't matter since frame of reference is an actual term here, there is no frame of reference more valid than any other for determining the linear or angular velocity or the position of a black hole.
Also,
> Two black holes who differ only by their ... angular momentum ... are not distinguishable
is contradicted by
> Two black holes who differ in ... spin ... are distinguishable
(Spin) Angular momentum is J in my first line above.
These are independent quantities.
See §5.11. ANGULAR MOMENTUM in Misner, Thorne & Wheeler (MTW) and in particular Box 5.6 D (Intrinsic Angular Momentum) and E (Decomposition of Angular Momentum into Intrinsic and Orbital Parts). The latter gives J = L + S. Admittedly, in MTW §33 the authors prefer to use S (e.g. eqn. 33.4) but that raises the important caveat for binary black hole (BBH) mergers at the end of Box 33.4 (I)(A)(4), which refers back to Box 5.6). Newer textbooks and other sources (including Wikipedia [1]) prefer J, although commonly it gets called spin angular momentum (as in [1] and my earlier comment). Carroll's textbook calls it the Komar angular momentum (near eqn. 6.73, referring to eqn. 6.48) and "spin (angular momentum)" (above eqn. 6.47). This is the sort of thing that annoys mathematicians and non-relativist physicists about relativists; confusion is completely understandable.
A binary black hole (BBH) is not a Kerr solution. No exact analytical solutions to the Einstein Field Equations for a BBH have been found, only approximations and numerical solutions (see the comprehensive review by Baker et al. at <https://arxiv.org/abs/1010.5260> and \vec{L} therein, notably at section D(2) in the second column on PDF p. 26, "In a related phenomenon, the direction of the total angular momentum (\vec{L} + \vec{S}_1 + \vec{S}_2) may change.").
No change of coordinates can turn a BBH into a Kerr solution; the former radiates gravitational waves (if there is no incoming gravitational radiation), the latter doesn't.
(Another way of distinguishing is in the algebraic symmetries of the Weyl curvature tensor. Kerr is a Petrov type D spacetime, BBH spacetimes are generically type I up to some degeneracy measure.)
Finally, I can tie this in to neutron stars: the (exterior) Hartle-Thorne metric is an approximation of the Kerr metric useful for relativistic stars without horizons (neutron stars, white dwarfs) and without regard to interior differentiation. Its usual write-down uses J, but sometimes S, and sometimes both (e.g. <https://arxiv.org/abs/1507.04264>, where at the top of p. 2 the authors give J = GS/c^3).
[1] <https://en.wikipedia.org/wiki/Kerr_metric#Overview>, "J represents its spin angular momentum" and see eqn (6) further down, "a = J/Mc".
https://www.vttoth.com/CMS/physics-notes/311-hawking-radiati...
If we switch the units to kg, we see that a mass of 278000 kg (139 metric tons) has a lifetime of about 1 second. That's a rounding error for something with a mass of the sun, or 2x10^30 kg.
I wonder if there's a black hole oscillating in and out of existence at the center of neutron stars, creating a resonance that might be detectable.
Also as a thought experiment, we could imagine dropping 1 more atom into a neutron star on the brink of total collapse. The star would start running down the "drain" of the black hole, red shifting away from us beneath its event horizon. We'd see it grow redder and redder, dimmer and dimmer as it recedes from us, while staying the same size due to the holographic effect of black holes. If we jumped in after it, the red shift would stay the same because we could never reach the star, but we'd experience severe tidal forces until we're ripped into spaghetti. Our clock would stay synced with an observer on the outside as we fall along the geodesic without outside forces acting upon us. Space just gets added between particles, which creates the red shift. I believe that passing the singularity means coming out the other side in a white hole exploding outward like the inflation at the start of our Big Bang, but nobody knows. We're just not good at thinking about space expanding at faster than the speed of light yet. That might limit the spaghettification to some proportion of the event horizon radius and make the journey survivable for atoms in a billion solar mass black hole, but who knows.
I'd like to see better proofs around stuff like neutron degeneracy pressure and the strong force. Electron degeneracy pressure is straightforward to understand from quantum mechanics, but I don't know if there's direct measurement of the strength of neutron repulsion from particle accelerators. Maybe the value they're using is empirical from the stars they've observed.
The way I think of it now is that neutron stars evaporate too, so if one is on the brink of collapse, we'd have to add enough mass to overcome that rate of loss and also get the black hole lifetime long enough that it goes into runaway collapse. Otherwise its mass will go back to decreasing slowly. Although if you look at the note at the bottom of the link, it states that objects heavier than 0.75% of Earth's mass are growing heavier due to absorbing the cosmic microwave background energy. So maybe all neutron stars eventually collapse on their own trillions of years from now.
Some other interesting ideas come out of that, like the center of a neutron star is probably nearly frozen in time as it withstands the flow of space into it. Like in the movie Interstellar where every hour on the water planet equates to 7 years in orbit. Or here on Earth where GPS systems have to compensate for time running slower for us on the surface. The center would also be nearly infinitely contracted by its Lorentz transformation, so the space around it would look thin to us outside but be normal thickness from its point of reference. So in a very real way, there's more space inside the star than we see from its radius. So much in fact that the center can be thought of as being nearly infinitely far away, even lightyears away. So spaghettification may make it so neighboring neutrons don't feel as squeezed along the radial axis as those nearer to the surface. Or maybe there's a stagnation line where gravity forms a dimple in spacetime, but if the density gets too high, the line advances inward until it reaches the center and tears through to form a singularity.
But see, we'd have to wait an eternity for the tear to occur from our frame of reference, which suggests that black holes never actually form. They just get deeper and slower, mimicking black hole physics if we think of them as a black box, but behaving differently inside than our intuition suggests.
I think modern physicists tend to prune ideas too early as being untenable or already explored. So they haven't thought through these sorts of edge cases enough. For example, we may not be able to actually reach a singularity by falling in. It's so small that we may end up missing and orbiting instead. That might have ramifications for quantization of the strong force or could explain why mass forms clouds instead of collapsing into points, and relate to String Theory (which I'm not fond of, but is worth mentioning). I have so many basic questions like these that it's hard to reason about this stuff without it feeling like hand waving. And since nobody can point to a definitive answer, these lines of questioning are still valid and worth pursuing IMHO.
Edit: I'm still not entirely sure about the 4th paragraph and how distance to the center works. If we think of neutrons near the center as sitting on platforms, nearly frozen in time, and we could fall in without hitting anything (like a neutrino) then when would we reach the sitting neutrons? Would it take a long time to get to them (lightyears), or would we sail on past (in about 1/10 of a light second) with our clock synced to someone outside since we never hit anything?
I’m admittedly no astrophysicist, but I’m pretty sure you mean 278 metric tons.
1 metric ton is 1000 metric kilos. We metricists like things simple :)
E.g.: Do they grow outward from a point? A true mathematical point, or a tiny by finite highly curved region? Does the matter "fall in", or does the event horizon "expand to encompass the existing matter"? Does the observer's perspective matter? I.e.: is there a scenario where from one frame there is a black hole seen but from another frame it's just very dense stuff?
The latter, where "tiny" for a stellar black hole is on the order of kilometers.
> Does the observer's perspective matter? I.e.: is there a scenario where from one frame there is a black hole seen but from another frame it's just very dense stuff?
An outside observer will never actually see light emitted at the moment the black hole forms: the infalling matter will just appear more and more heavily redshifted until it becomes undetectable.
As for the fabric/whitehole idea, I am in that camp if wormholes are a provably a thing, than hawking radiation over cosmic timescales could cause the eventual death of the singularity. Though if wormholes are provably a thing, then whiteholes would just be the other end. I wonder the black hole object fully evaporates or are there chunks of ancient black holes just floating around.
Tangent: would not 278000 kg be 278 metric tons, i.e., tonne?
Honestly, I got lost part of the way through.
It isn't just a guess that these things have some similarity, our theories very confidentally tell us that both situations are best described as QCD matter. The properties of this QCD matter, including the equation of state, is the fundamental science question that is of interest here.
Unless...the galactic core is above us :)
As huge as gravity is (making everything basically two-dimensional shapes on the surface), the magnetic forces are formidable, too, forcing inhabitants to be oriented and moving only in certain directions.
Is there any way to generate/accumulate/study cold neutrons? I assume they don't like to stick together. For example, the polyethylene brick shielding use on many fusors, it it accumulating free neutrons?
Unfortunately because of the 10.3 minute half-life of free neutrons, this is a hideously radioactive gas that is dangerous to be anywhere near.
The highest medical magnets used for MR currently go up to 7T.
You’re not alone. Grand unification theories [1] like supersymmetry are motivated by unifying the strong and electroweak forces [2][3].
> along with some relativistic effects
This is theory of everything [4] talk. We don’t know enough about gravity to speak coherently about it.
[1] https://en.m.wikipedia.org/wiki/Grand_Unified_Theory
[2] https://en.m.wikipedia.org/wiki/Electroweak_interaction
[3] https://openstax.org/books/physics/pages/23-3-the-unificatio... read me first
>> This is theory of everything [4] talk. We don’t know enough about gravity to speak coherently about it.
I would assert that there is an electrostatic equivalent of gravitational black holes. In my world, quarks exist inside an event horizon within a baryon and that's part of what keeps it stable. The other part being electrostatic attraction of course:
+2 -1 +2 << this configuration of charges will attract. Orbiting at speed C will help, and will also create a magnetic field. What keeps it dynamically stable forever though... I dunno.
If not, I, don’t see what’s wrong with their claim?
The electromagnetic field tensor is the real object here. The electric and magnetic fields are artifacts of a particular choice of coordinate system.
I thought I read the strong force also dropped like 1/r^3, but also that it was very hard to characterize it at all.
Shouldn't this read "ultra-high"?
Who proof-reads these things?