How Does the Size of Neutron Stars Compare to Black Holes?

  • #36
davLev said:
Therefore, how billions over billions of neutrons could keep their properties/mass while they all collapse into a Black hole and occupy the same quantum state/same space?
Drakkith said:
They can't.* That's one of the things we don't know about black holes. We don't know what happens to matter that falls inside. It's unlikely that it simply disappears, as that would violate various conservation laws.
Thanks

Do appreciate your reply.

As the matter can't occupy the same quantum state/same space without breaking the law of science, then why do we insist for a singularity in a BH?

Why can't we agree that even BH should have some sort of internal space/radius?

Drakkith said:
Our best explanation is that the black hole evaporates slowly over time via hawking radiation but what exactly happens to matter that falls into the black hole is unknown at this time.

What about SMBH and quasars?
Do we believe that all of them evaporate slowly over time via hawking radiation?

Drakkith said:
*Note that mass is conserved, even when particles change into other particles. The mass of the protons and electrons that combine during supernovas to form the neutrons that make up the neutron star is not lost. It goes into forming the neutrons. The same thing would happen if neutrons are forced to change into something else. Their mass would go into that new system.
Neutron is a composite particle (3 quarks and gluons)

All the 3 quarks contribute only 1% to its mass, while the gluons contribute 99%.
As long as we keep the gluons inside the neutron / proton, then we also keep its total mass.

However, what could be the outcome of collapsing this composite particle?
We have an evidence that the "average peak pressure, near the center of the proton, comes out to 10^35 pascals"
However, do we know what is the "average peak pressure, near the center of the quark?
Could it be that the average peak pressure of the quarks is higher than this value of 10^35?

If so, why can't we assume that if the pressure crosses the 10^35 pascals (but not high enough to break the quarks) then the neutron would be broken to its composite particle - quarks and gluons.
Could it be that the gluons mass would be lost once it is outside the neutron but the quark mass would be kept?

In that article it is stated:
The Surprising Reason Why Neutron Stars Don't All Collapse To Form Black Holes
They also specifically discuss about quark star.
"a neutron star or even a strange quark star are all still made of fermions."

If we add the impact of the spinning motion on the total gravity, could it be that Black hole is actually massive neutron (or quark) star which must have some sort of minimal radius?
 
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  • #37
davLev said:
This textbook was published in 1983.
Yes.

davLev said:
For me, evidence means observation.
I wonder what kind of observation Shapiro & Teukolsky have used to justify their theoretical astrophysics of Compact Objects?
Read the book and see. If you are under the impression that there was no such evidence in 1983, you are egregiously mistaken.

davLev said:
If the rotation of the neutron star is almost at the speed of light, could it decrease dramatically the total gravity?
If you would go and read Shapiro & Teukolsky, you would see that they discuss exactly this case. The answer is no, it won't decrease "dramatically" gravity, and it won't increase "dramatically" the maximum mass. Nothing that has been discovered since has changed that.
 
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  • #38
davLev said:
Based on the above law of physics it is impossible for two neutrons to occupy the same quantum state/same space.
Therefore, why can't we claim that if we break the Neutrons, we also break their properties?
If you "break" neutrons, you get quarks. Which are still fermions.

davLev said:
As the matter can't occupy the same quantum state/same space without breaking the law of science, then why do we insist for a singularity in a BH?
Nobody "insists" on a singularity inside a BH. In fact, most physicists believe that the fact that GR predicts a singularity inside a BH means that GR is an incomplete theory, and is expected to be replaced by a more fundamental theory, probably some form of quantum gravity, in the regime where spacetime curvature reaches the Planck scale.

However, that regime is still far inside a black hole, and has nothing to do with the event horizon and the physics in that regime. Nor does it have anything to do with the maximum mass limits on white dwarfs and neutron stars. In other words, it in no way changes the prediction of formation of black holes by gravitational collapse. It only changes what might be deep inside black holes once they are formed.

davLev said:
Why can't we agree that even BH should have some sort of internal space/radius?
A BH is not a point. It does have spacetime inside it. You do not appear to have a good grasp of what our models of black holes actually say.

davLev said:
What about SMBH and quasars?
Do we believe that all of them evaporate slowly over time via hawking radiation?
That is the current belief, yes. However, we have no evidence of such evaporation, nor do we expect to get any any time soon. Indeed, even without any other matter or radiation falling into a black hole, the CMBR temperature is higher than the Hawking temperature of all the black holes we have observed, so those holes right now, and for a very, very long time in the future, will not be evaporating, they will be very slowly gaining mass as CMBR radiation falls into them.
 
  • #39
davLev said:
he neutron would be broken to its composite particle - quarks and gluons.
Could it be that the gluons mass would be lost once it is outside the neutron but the quark mass would be kept?
No. You evidently do not have a good understanding of the process you are talking about, or of gluons and quarks in general.

Gluons are massless; they have zero rest mass, just like photons. Their energy is entirely kinetic energy; how much of it they have depends on how small a volume they are confined to.

The "neutron breaking" you describe happens under extreme pressure, which means the quark-gluon plasma you get under these extreme conditions, when there is no longer any meaningful neutron structure, is confined to a very small space--the quarks and gluons that made up a neutron are actually confined to a smaller volume than they were when they made up a neutron. They don't go anywhere and they don't lose any energy; indeed, their energy per particle is higher than when they made up a neutron, because they are confined to a smaller space.

davLev said:
If we add the impact of the spinning motion on the total gravity, could it be that Black hole is actually massive neutron (or quark) star which must have some sort of minimal radius?
No. None of the references you give say any such thing.

Also, all the references you give are pop science articles. They are not good sources for learning actual science. You need to be looking at textbooks and peer-reviewed papers. All you are doing at this point is misinterpreting pop science articles that already aren't good descriptions of the actual science, and then asking uninformed questions. That is not a good way to learn science.
 
  • #40
PeterDonis said:
In fact, most physicists believe that the fact that GR predicts a singularity inside a BH means that GR is an incomplete theory, and is expected to be replaced by a more fundamental theory, probably some form of quantum gravity, in the regime where spacetime curvature reaches the Planck scale.
Wow!
PeterDonis said:
Nobody "insists" on a singularity inside a BH.

PeterDonis said:
A BH is not a point. It does have spacetime inside it.

Thanks
As you confirm that BH is not a singularity or a point and It does have spacetime inside it, then do you agree that BH must have some minimal space/volume/radius?
 
  • #41
davLev said:
As you confirm that BH is not a singularity or a point and It does have spacetime inside it, then do you agree that BH must have some minimal space/volume/radius?
No. It has spacetime inside it, but there is no "minimal" amount that it must have.
 
  • #42
davLev said:
As you confirm that BH is not a singularity or a point and It does have spacetime inside it, then do you agree that BH must have some sort of space/volume/radius?
That's... complicated. Per this article: https://arxiv.org/abs/0801.1734

The area of a Schwarzschild black hole is unique, and can be defined by an idealized transverse measurement of a particular spherical surface. In contrast, the volume inside a black hole requires a definition of the particular 3-space in which the volume is computed, which may be explicitly time dependent, and an understanding of the (possibly time dependent) limits of the integral required to compute this volume.
 
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  • #43
PeterDonis said:
No. It has spacetime inside it, but there is no "minimal" amount that it must have.

If it has spacetime, then how could it be that it has no space or volume?
Can you please explain the contradiction?

Please be aware that the number of atoms in the sun comes to 1.201×10^57.
Therefore, in a neutron star with one solar mass there should be at least 10^57 neutrons while a BH with one solar mass should have 10^57 neutrons mass.
SMBH could have 10^6 solar mass = 10^63 Neutrons/protons mass
Quasar could have 10^9 solar mass = 10^66 Neutrons/protons mass.

Therefore, why can't we agree that SMBH with 10^6 solar mass should have bigger volume than a BH with one solar mass (by about 10^6), while quasar should have a bigger volume than SMBH (by about 10^3)?

If you still disagree, then how can we fit the whole quasar mass (10^9 solar mass) in the same volume of a BH with a single solar mass?
 
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  • #44
davLev said:
If it has spacetime, then how could it be that it has no space or volume?
The volume of a black hole is not well defined. You can get different answers depending on how you choose to assess it. Having infinite interior volume is a perfectly reasonable answer, or it can vary with time.

You can define the surface area of the event horizon. You can derive a so-called "areal radius" from this using ##A=4\pi r^2##, but because the interior of the black hole is not Euclidean this is not "the distance to the center" (and "distance to the center" is an elusive concept inside the hole). Optically, from a distance it appears to be somewhat more than 1.5 times that radius due to the curvature of light rays.

The key point to realise is that what we call "the black hole" is the region inside the event horizon. There's no need for that region to be filled with matter. And the other key point to realise is that we do not know of any mechanism to stop the collapse of matter. Fermion degeneracy pressure (what you were talking about with two particles not wanting to occupy the same state) supports neutron stars. Once the pressure is too high for that to stop collapse we know of nothing else that can.

The result of allowing collapse to continue unchecked is the black hole singularity. Nobody thinks this is particularly plausible, but it's most likely a problem with general relativity - hence the search for a quantum theory of gravity. Simply saying (as you seem to be doing) "something must stop the collapse" is overly simplistic - we know we don't understand any of the rules right at the heart of a black hole.

Dragging this back to the original topic, we're pretty confident that we understand how big a black hole appears on camera, and it is fairly simply related to the mass and spin and independent of exactly what happens inside. Neutron stars are far more complicated because their size does depend on the details of what goes on inside. And those details are relatively poorly understood, so observational bounds on how they actually behave is useful in refining our models.
 
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  • #45
davLev said:
If it has spacetime, then how could it be that it has no space or volume?
I didn't say it has no space or volume. Go read what I said again.

davLev said:
Can you please explain the contradiction?
There is no contradiction. You are just not reading very carefully.
 
  • #46
davLev said:
why can't we agree that SMBH with 10^6 solar mass should have bigger volume than a BH with one solar mass (by about 10^6), while quasar should have a bigger volume than SMBH (by about 10^3)?
Because of the issue described in the paper @Drakkith linked to. Which boils down to what @Ibix said:

Ibix said:
The volume of a black hole is not well defined.
 
  • #47
Ibix said:
The volume of a black hole is not well defined.
Thanks for your comprehensive reply.

Please be aware that I didn't ask what is the volume, I have asked if BH has a volume.
If the Black hole is not well defined, then we have to agree that it could have a volume.
If we claim that a black hole has no volume, then by definition we defined the volume.

PeterDonis said:
I didn't say it has no space or volume. Go read what I said again.
As you have confirmed that a BH is not a point. It does have spacetime inside it, while you didn't say that BH has no space or volume, then can we at least agree that it could have a volume?

Ibix said:
Fermion degeneracy pressure (what you were talking about with two particles not wanting to occupy the same state) supports neutron stars. Once the pressure is too high for that to stop collapse we know of nothing else that can
If we wish to obey law of science then the understanding that "two particles not wanting to occupy the same state" should be valid to any kind of object including Neutron stars and BHs.

Ibix said:
The result of allowing collapse to continue unchecked is the black hole singularity. Nobody thinks this is particularly plausible, but it's most likely a problem with general relativity - hence the search for a quantum theory of gravity. Simply saying (as you seem to be doing) "something must stop the collapse" is overly simplistic - we know we don't understand any of the rules right at the heart of a black hole.
Did we ever observe a Neutron star as it collapse into BH?
As there might be a problem with general relativity, and as we know we don't understand any of the rules right at the heart of a black hole, then could it be that there is an error with the assumption of singularity in a BH?

Ibix said:
Neutron stars are far more complicated because their size does depend on the details of what goes on inside.

A question with regards to Neutron star:
The event horizon radius for any one solar mass object is fully defined = 3Km.
https://www.astro.ucla.edu/~ghezgroup/gc_edit/Latest/faq.html
The event horizon is 3km (a little less than two miles) for our Sun, or any one-solar-mass object. For more massive black holes, the size of the event horizon scales linearly; ten-solar-mass black hole would have a 30-km event horizon.

That definition works for a BH and Neutron star (with one solar mass).
The radius of the neutron star is also fully defined = 10Km.
https://www.toppr.com/ask/question/...and-a-neutron-stareach-of-one-solar-mass-the/
The radius of the neutron star with one solar mass is 10 km.

As we have full definition for the radius of Neutron star (10Km) and its event horizon (3Km), then would you kindly explain why we can't see its surface which should be located outside the event horizon?

As we can't see the surface of a Neutron star although its radius is bigger than the event Horizon, then could it be that we have an error in our definition about Neutron star?
 
  • #48
davLev said:
Please be aware that I didn't ask what is the volume, I have asked if BH has a volume.
The answer is that the volume of a black hole is not well-defined.

davLev said:
If the Black hole is not well defined
Nobody said a "black hole" is not well-defined. It is. What is not well-defined is the volume of a black hole.

davLev said:
then we have to agree that it could have a volume.
"Not well-defined" doesn't mean "might have a volume or might not". It means that, given a particular black hole, there is no one unique number that is the "volume" of the hole. You can get pretty much any number greater than zero and less than infinity, depending on how you define "volume". There is no one unique answer.

davLev said:
If we claim that a black hole has no volume
Nobody has claimed that. Again, you need to read more carefully. You keep responding to things that nobody has said, and you do not appear to be properly comprehending what people have said.

davLev said:
If we wish to obey law of science then the understanding that "two particles not wanting to occupy the same state" should be valid to any kind of object including Neutron stars and BHs.
BHs are not made of fermions, so no, this is not valid for BHs. It is valid for matter made of fermions that collapses to a black hole, but the black hole itself is not the same thing as the matter that collapsed to form it.

davLev said:
Did we ever observe a Neutron star as it collapse into BH?
Not directly, no. But there is plenty of indirect evidence to support our best current models of such a process.

davLev said:
As there might be a problem with general relativity
There is no such problem with regard to the process of a neutron star (or any other object) collapsing to a black hole.

davLev said:
as we know we don't understand any of the rules right at the heart of a black hole,
That's not correct. We do have a set of rules; that set of rules predicts that the matter that collapses to form a black hole collapses to zero size and is destroyed in a singularity.

Many physicists hypothesize that this prediction of GR means that GR is an incomplete theory, and that at very large spacetime curvatures, encountered just before GR predicts that there is a singularity, GR breaks down and some other theory, presumably some form of quantum gravity, takes over. But this is a hypothesis. It's not a proven fact and there is no evidence which requires us to consider it. It's just a theoretical issue that many physicists believe will have to be resolved at some point. That's all it is.

davLev said:
could it be that there is an error with the assumption of singularity in a BH?
See above.

davLev said:
That definition works for a BH
Yes.

davLev said:
and Neutron star (with one solar mass).
No. A neutron star (or any other object that is not a black hole) has no event horizon, and the "Schwarzschild radius" calculation is physically meaningless for such an object.

davLev said:
would you kindly explain why we can't see its surface which should be located outside the event horizon?
Nobody has claimed that we cannot see the surface of a neutron star. You can't see the surface of a black hole.
 
  • #49
@davLev at this point I am closing this thread. You keep "responding" to claims that nobody has made; you are not reading what people have said carefully; and you keep referencing pop science sources instead of going and looking at textbooks or peer-reviewed papers to learn the actual science. At this point the actual substantive questions you have asked have been thoroughly responded to.

I strongly suggest that you take some time to learn the relevant science from valid sources before posting about this subject again.

Thread closed.
 
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