Exploring Black Hole Anatomy: The Singularity, Event Horizon, and Photon Sphere

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Discussion Overview

The discussion revolves around the anatomy of black holes, specifically focusing on the singularity, event horizon, and photon sphere. Participants explore theoretical aspects, mathematical relationships, and speculative models regarding the nature and properties of these components within the framework of general relativity and beyond.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants note that singularities are not well described by modern physics, with general relativity providing nonsensical answers at the singularity itself.
  • There is mention of the Schwarzschild radius as a basic relationship for calculating distances and ratios between the event horizon, photon sphere, and singularity.
  • Questions arise about whether the singularity has an actual size or diameter, with some proposing that it could have a finite density and therefore a measurable size.
  • Some participants argue that the singularity must be a point of infinite density, while others suggest that it could be modeled differently, potentially allowing for a finite size.
  • Concerns are raised about the reliability of general relativity in describing black hole behavior, particularly inside the event horizon.
  • There is speculation about whether a singularity could be so dense that it cannot collapse further, leading to questions about the need for pressure to prevent collapse.
  • Some participants discuss the implications of fundamental particles and their sizes in relation to the density of a singularity, suggesting that as density increases, the concept of size becomes less clear.
  • There are references to alternative theories, such as string theory, which might provide insights into the nature of singularities.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the nature of singularities, their potential size, and the applicability of general relativity. The discussion remains unresolved, with no consensus on the fundamental properties of singularities or the calculations related to them.

Contextual Notes

Limitations include the dependence on general relativity for calculations, the unresolved nature of singularities, and the speculative aspects of alternative theories. The discussion highlights the complexity and uncertainty surrounding the topic.

  • #31
zhermes said:
Yes, the singularity is of course an issue---but I don't see how adding a finite-aged black-hole complicates the issue. And note that you don't have evaporation with just general relativity.
The potential complication is that it is apparently unknown whether or not a singularity would form for a finite-aged black hole (in this case singularity simply meaning dense clump of matter at the center, instead of a mathematical singularity, since we'd be talking about a real black hole). That is, the time dilation may be so severe that the matter inside the event horizon just doesn't have enough time to collapse any significant amount before the black hole evaporates.

And yeah, obviously I was talking about a semi-classical black hole with regard to evaporation, which uses General Relativity to define the space-time but adds an evaporation mechanism.
 
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  • #32
Chalnoth said:
The potential complication is that it is apparently unknown whether or not a singularity would form for a finite-aged black hole (in this case singularity simply meaning dense clump of matter at the center, instead of a mathematical singularity, since we'd be talking about a real black hole). That is, the time dilation may be so severe that the matter inside the event horizon just doesn't have enough time to collapse any significant amount before the black hole evaporates.
This is not an issue. Formation of black-holes and singularities has been thoroughly studied, by Papapetrou, Thorne, Penrose... Teukolsky I think. Again, in all astrophysically significant cases, evaporation can't occur----absorption of the CMB is far more rapid than the production of hawking radiation (and I can't recall for sure, but I think even very low ambient density environments, the bondi accretion is also more rapid than Hawking Radiation).
 
  • #33
zhermes said:
This is not an issue. Formation of black-holes and singularities has been thoroughly studied, by Papapetrou, Thorne, Penrose... Teukolsky I think.
Well, admittedly I haven't looked into this in great detail myself. But in this case I'm going off of my GR professor, Steve Carlip, who I think is generally quite good on this stuff. As far as I know, we're still a long way from really examining what GR has to say here for anything beyond the absolute simplest case. My understanding was that the only sort of black hole formation we could produce was due to symmetric infalling spherical shells, and that is a highly non-physical situation.

zhermes said:
Again, in all astrophysically significant cases, evaporation can't occur----absorption of the CMB is far more rapid than the production of hawking radiation (and I can't recall for sure, but I think even very low ambient density environments, the bondi accretion is also more rapid than Hawking Radiation).
Well, sure, but those accretion processes will all end in far, far less time than the expected black hole evaporation rate anyway. We're talking roughly 10^{66} to 10^{100} year timescales here. So I don't quite understand what this has to do with my point that we may not know much of anything about what's going on inside the black hole's event horizon.
 
  • #34
Chalnoth said:
At the very least, the photon, gluon, W and Z bosons, and the Higgs boson.

Chalnoth, are Bosons or force carriers conidered what is loosely called "ponderable matter". I am quite prepared to be wrong about this I just thought they werent.
 
  • #35
Tanelorn said:
Chalnoth, are Bosons or force carriers conidered what is loosely called "ponderable matter". I am quite prepared to be wrong about this I just thought they werent.
Well, they are either moving at the speed of light or are unstable. But when they are inside the event horizon of a black hole, moving at the speed of light doesn't prevent collapse, and the extreme space-time curvature may potentially make the W and Z bosons stable, in an analogous way to how the incredibly high pressure inside a neutron star makes neutrons stable.

Edit: Of course, this almost certainly isn't enough to produce a degenerate bosonic state at the center of a black hole, because you also have to get rid of the baryons, and baryon number is a conserved quantity in known physics. So we would probably need some beyond-standard-model interactions to get into a degenerate bosonic state, and that may open the door for still more bosons.
 
  • #36
It was specifically in reference to your comment that:
Chalnoth said:
That is, the time dilation may be so severe that the matter inside the event horizon just doesn't have enough time to collapse any significant amount before the black hole evaporates.
Those studies have shown singularity formation in finite coordinate (and proper) time---but you're right, I'm not sure exactly how long (but I think its on the order of a dynamical time), and in how diverse situations; good keeping me on my toes.

But going back to the initial point; the event horizon can definitely form stably. We agree that the singularity itself is completely questionable---so that part doesn't really matter. My overall argument is that we are really really confident event horizons can form; and quantum mechanics (string theory etc etc) only suggest GR breaks something like 50 orders of magnitude closer to the center of the BH than the event horizon... so there doesn't seem to be a reason to expect GR to break near the EH...

(Unless you're looking at a near-extremal kerr black-hole---which we believe exist---in which case the singularity itself can be very near the event horizon.
 
  • #37
zhermes said:
The nature of the material within the event horizon doesn't matter in general relativity.
Mabey not in GR but it does matter to the anatomy of black holes and the point of this conversation. GR has trouble explaining some things and obviously black holes are one of them.



zhermes said:
There is no such thing as 'a particle so much smaller than anything else'---
How can anyone say there are no particles smaller. Didn,t they original name the atom becuase they thought it could not be divided anymore? We know quarks are made from something smaller, maybe that will be the next think we discover.
 
  • #38
bill alsept said:
Mabey not in GR but it does matter to the anatomy of black holes and the point of this conversation. GR has trouble explaining some things and obviously black holes are one of them.
I've already told you the answer according to string theory; nothing else applies.

bill alsept said:
How can anyone say there are no particles smaller. Didn,t they original name the atom becuase they thought it could not be divided anymore? We know quarks are made from something smaller, maybe that will be the next think we discover.
Quarks are not made of something smaller---they are fundamental particles. Fundamental particles are points---i.e. no finite size--and thus, again, nothing can be smaller. Additionally the concept of 'size' of a particle doesn't really apply in this regime (unless you're talking about string theory), and as I said before, in that case you have a Planck-sized mass at the center of the (schwarschild) black-hole.
 
  • #39
zhermes said:
I've already told you the answer according to string theory; nothing else applies.

I'm sorry but that sounds to much like a religious answer. The nature of the material within the event horizon would matter. If like you say it doesn't matter to GR then who cares. It’s still there and would matters to everything else.

Why do black holes need to be so mysterious? Why can't they just be like every other mass. Just because g has an escape velocity faster than light who cares. Everything is still there we just can't see it. If we ever find a way to see black holes I would bet that the body of the black hole has an actual diameter and that its growing.
zhermes said:
Quarks are not made of something smaller---they are fundamental particles. Fundamental particles are points---i.e. no finite size--and thus, again, nothing can be smaller. Additionally the concept of 'size' of a particle doesn't really apply in this regime (unless you're talking about string theory), and as I said before, in that case you have a Planck-sized mass at the center of the (schwarschild) black-hole.

You can't say quarks are fundamental without proof. We may one day find that there are many smaller levels. I think one clue that quarks are made of smaller parts is that quarks react with other quarks. Whatever force they use to accomplish this may come from within each one so they could have some sub parts or moving parts to cause these forces, fields or phenomenon. Just a thought
 
  • #40
  • #41
bill alsept said:
You can't say quarks are fundamental without proof.

Mathematicians deal with proof. Physicists deal with evidence.

The reason we know that protons are not point particles is that if you ram two protons together you get scattering angles that are consistent with sub-structure. If you ram quarks and electrons together, you get scattering that is consistent with point particles.

Also thermodynamics and QM provide some limits on the types of viable preon models.

http://en.wikipedia.org/wiki/Preon

Essentially if quarks had substructure, the Heisenberg uncertainty principle would cause enough momentum uncertainty to be larger than the rest mass of the particle. There are also thermodynamic limits. If you have substructure you change the statistics of matter and so that changes its thermal properties.

There are ways of getting around those limits, but right now the experimental data is consistent with non-substructure and there are some very strong limits as to what theories are consistent with observations.

We may one day find that there are many smaller levels.

We've looked. We haven't found anything, and we have evidence that there is nothing there to be found.

I think one clue that quarks are made of smaller parts is that quarks react with other quarks. Whatever force they use to accomplish this may come from within each one so they could have some sub parts or moving parts to cause these forces, fields or phenomenon. Just a thought

Look up "preon"
 
  • #42
bill alsept said:
How can it collapse further and why does it have to? Can't a black hole be so dense that there is no space left inside? An area filled 100% complete with the smallest partials the universe has to offer. There would be no more area to collapse to.

Won't work. What happens is that as you increase the gravity, the number of possible energy states for the particles increase so that the pressure necessary to keep the particles from collapsing disappears.

This is a general argument that works with any set of particles.

I realize my original question most likely cannot be answered because we don’t know how small those first particles are or how many have accumulated in the black hole.

Doesn't matter, the smaller the particles, the faster the collapse. As long as special relativity is correct, then given enough gravity, things are unstable to collapse. If special relativity is wrong, then you tell me what the rules are.
 
  • #43
bill alsept said:
I understand pressure is required to supports a balloons surface but not so simple on a bowling ball. Why is pressure needed on a complely solid object?

Pressure is what makes a solid object a solid.
 
  • #44
twofish-quant said:
Mathematicians deal with proof. Physicists deal with evidence.

The reason we know that protons are not point particles is that if you ram two protons together you get scattering angles that are consistent with sub-structure. If you ram quarks and electrons together, you get scattering that is consistent with point particles.

Also thermodynamics and QM provide some limits on the types of viable preon models.

http://en.wikipedia.org/wiki/Preon

Essentially if quarks had substructure, the Heisenberg uncertainty principle would cause enough momentum uncertainty to be larger than the rest mass of the particle. There are also thermodynamic limits. If you have substructure you change the statistics of matter and so that changes its thermal properties.

There are ways of getting around those limits, but right now the experimental data is consistent with non-substructure and there are some very strong limits as to what theories are consistent with observations.



We've looked. We haven't found anything, and we have evidence that there is nothing there to be found.



Look up "preon"

Thank You for good answers.
 
  • #45
bill alsept said:
Maybe the smallest particles in the universe only have space between them because they are each liberated and going through some repeated cycles of their own. When they are finally corralled and pushed together to the point they can no longer be liberated or move they loose any effect or phenomena they caused before.

That makes things worse.

The reason that solids are solids is because you've filled up all of the available energy states and to kick a particle into a higher energy state takes a lot of energy. If you create additional particles, then you increase the number of energy states, and things become softer.

One way of thinking about this is imagine getting hit by a brick. And getting hit by a pile of sand. Because there are more ways that the sand can move, it's a lot softer, and this sort of thing happens at the subatomic level.

Could it even be possible that a black hole goes completely cold at the center? And would need no support again leading to the idea that the singularity may have a diameter instead of being a point?

When you have no evidence then anything is possible. It's possible that the black hole goes completely cold. It's also possible that the singularity turns into trained dancing penguins. When you don't know, you don't know.
 
  • #46
bill alsept said:
Sorry, I am not trying to beat a dead horse here but I am talking about after neutron degeneracy pressure of the neutron star and any other stages of collapse a body of mass may go through including the stage of converting to a black hole. Which I think is the same as all the other stages where the escape velocity just rises another notch. In this case it rises above the speed of light. But after that stage what stages are there and eventually you get to a particle that are so much smaller than anything else. There would be no other place to collapse to.

Small particles makes things collapse faster. The reason things stop collapsing is that you've filled up all of the energy states. Once you increase gravity, the energy levels change so that you have empty stops that open up. If you create new particles, the number of energy states increases even more so things will collapse faster.
 
  • #47
bill alsept said:
Why do black holes need to be so mysterious? Why can't they just be like every other mass.

I don't think that black holes are mysterious. The singularity in the middle of a black hole, on the other hand...

Just because g has an escape velocity faster than light who cares. Everything is still there we just can't see it. If we ever find a way to see black holes I would bet that the body of the black hole has an actual diameter and that its growing.

There's a basic problem.

Suppose you have an infinitely stiff stick. I push the stick on earth, then instantly the end of the stick on the moon moves. Uh. Oh. I just transmitted information faster than light, and that's a no-no. So the speed of light puts limits on how stiff something is.

So let's think of something else. I hit a table. The atoms in the table change directions and creates a force that pushes back. Now let's suppose I have something that is traveling near the speed of light. Since I can't push it past the speed of light, if I push on something that near the speed of light, it doesn't change speed very much. No matter how much energy I put into it, it won't go past the speed of light.

This presents a problem. Suppose I have a table and the particles in it are vibrating at close to the speed of light. If I hit that table, the particles won't react, and so I won't get a force in the other direction. So if I hit a table with particles moving at close to the speed of light, then my hand will fall through the table, and since the particles don't react with each other, solid objects are impossible once you have particles that are moving at close to light speed.

So the net result is that it doesn't matter what the table is made of. It doesn't matter how many particles there are. Once I crush the table enough so that the particles are moving near light speed, it will cease acting like a solid object. Having smaller particles makes the problem *worse* since it's easier to push a particle to light speed.

This means that if Einstein is right, things will get crushed to nothing. Now this leads to some absurd situations, so we are pretty sure he is wrong. The trouble is that no one knows *how* he is wrong.
 
  • #48
twofish-quant said:
I don't think that black holes are mysterious. The singularity in the middle of a black hole, on the other hand...
There's a basic problem.

Suppose you have an infinitely stiff stick. I push the stick on earth, then instantly the end of the stick on the moon moves. Uh. Oh. I just transmitted information faster than light, and that's a no-no. So the speed of light puts limits on how stiff something is.

So let's think of something else. I hit a table. The atoms in the table change directions and creates a force that pushes back. Now let's suppose I have something that is traveling near the speed of light. Since I can't push it past the speed of light, if I push on something that near the speed of light, it doesn't change speed very much. No matter how much energy I put into it, it won't go past the speed of light.

This presents a problem. Suppose I have a table and the particles in it are vibrating at close to the speed of light. If I hit that table, the particles won't react, and so I won't get a force in the other direction. So if I hit a table with particles moving at close to the speed of light, then my hand will fall through the table, and since the particles don't react with each other, solid objects are impossible once you have particles that are moving at close to light speed.

So the net result is that it doesn't matter what the table is made of. It doesn't matter how many particles there are. Once I crush the table enough so that the particles are moving near light speed, it will cease acting like a solid object. Having smaller particles makes the problem *worse* since it's easier to push a particle to light speed.

This means that if Einstein is right, things will get crushed to nothing. Now this leads to some absurd situations, so we are pretty sure he is wrong. The trouble is that no one knows *how* he is wrong.

Thank you, I like the way you describe things. Very insightful and interesting. I too think there is a problem and would like to discuss this more but it seems I get scolded every time I even begin to get speculative. Thanks again
 
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  • #49
twofish-quant said:
Small particles makes things collapse faster. The reason things stop collapsing is that you've filled up all of the energy states. Once you increase gravity, the energy levels change so that you have empty stops that open up. If you create new particles, the number of energy states increases even more so things will collapse faster.

Can you explain this one another way?
Thanks
 
  • #50
twofish-quant said:
There's a basic problem.

Suppose you have an infinitely stiff stick. I push the stick on earth, then instantly the end of the stick on the moon moves. Uh. Oh. I just transmitted information faster than light, and that's a no-no. So the speed of light puts limits on how stiff something is.



I know this is speculating (not overly I hope) but what if the speed of light was not the end all. What if that’s all the faster it could go because of some unknown resistance. It appears gravity out does the speed of light why not other things?
 
  • #51
bill alsept said:
I know this is speculating (not overly I hope) but what if the speed of light was not the end all. What if that’s all the faster it could go because of some unknown resistance. It appears gravity out does the speed of light why not other things?
Given that we have experimented with many particles moving exceedingly close to the speed of light, it is highly highly unlikely that we are misunderstanding this effect.
 
  • #52
Why can't this work?

http://scienceblogs.com/startswithabang/2009/11/a_black_hole_without_a_singula.php
 
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  • #53
bill alsept said:
Why can't this work?

http://scienceblogs.com/startswithabang/2009/11/a_black_hole_without_a_singula.php
I strongly suspect that the pressure wouldn't allow it to keep from collapsing further, as before.
 
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  • #54
I tend to agree with Bill, the idea of a singularity just does not make sense. Why cannot a neutron star be massive enough or small enough to create a black hole. The smallest particle must be incompressible beyond some level of pressure.
 
  • #55
PRDan4th said:
I tend to agree with Bill, the idea of a singularity just does not make sense. Why cannot a neutron star be massive enough or small enough to create a black hole. The smallest particle must be incompressible beyond some level of pressure.
Why?
 
  • #56
A neutron star can grow by accumulating more stars and become more massive enough to increase the gravity at the event horizon, thus becoming a black hole. This does not require it to become infinitely small. This, of course, is just my opinion. I cannot accept the idea of a singularity, regardless of what Einstein said.
 
  • #57
PRDan4th said:
A neutron star can grow by accumulating more stars and become more massive enough to increase the gravity at the event horizon, thus becoming a black hole. This does not require it to become infinitely small. This, of course, is just my opinion. I cannot accept the idea of a singularity, regardless of what Einstein said.
Well, no, we can be quite certain there is no such thing as a singularity. However, the answer cannot be related to pressure, because once you go beyond a certain density, greater pressure simply causes a greater gravitational field, so that collapse becomes inevitable.

The only way this can be resolved is through a quantum theory of gravity.
 
  • #58
Matter is energy... and energy does not, to my knowledge, have the space restrictions matter has.
So when gravity is strong enough then matter turns into energy and can occupy an infinitely small volume. (Where only quantum theory sets a limit.)
 
  • #59
When matter turns into energy it gives off a great deal of heat! Think A-bomb. If a neutron star collapsed to a point by convert into energy the heat released would blow it apart. So I do not think this works.
 
  • #60
PRDan4th said:
When matter turns into energy it gives off a great deal of heat! Think A-bomb. If a neutron star collapsed to a point by convert into energy the heat released would blow it apart. So I do not think this works.
I was thinking of a black hole...i don't think neutron stars can collapse.
 

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