B Are Black Holes Actually Giant Neutron Stars Cloaked in an Event Horizon?

[Drakkith]

How can you say with certainty that there is no physical surface beyond the event horizon?

No one is saying with certainty that there isn't a physical surface beyond the EH. What they're saying is that according to the rules of General Relativity there shouldn't be one.

 

[MichaelMo]

How can you say with certainty that there is no physical surface beyond the event horizon? That's mostly why I asked the question. I know I veered off with my analogy, but really, how do we know it's not a super compact body?

IMO, you're definitely asking the right questions. :) You might also take a gander at the Pauli exclusion principle and consider the fact that black holes can supposedly hold a charge. We don't really know what might exist below the event horizon, but the Pauli exclusion principle should preclude anything from achieving infinite density.

I read somewhere about the interior of neutron stars described as disassociated particle soup and that led me to this question. I've read smarter people than me (not a high bar) who refer to infinites as indications the mathematical representation of a particular phenomenon is flawed. Suggesting that different equations are needed to accurately discribe it. It all just really peaks my curiosity.

Great! :) It's awesome when something in science piques your curiosity. :)

 

[MichaelMo]

No one is saying with certainty that there isn't a physical surface beyond the EH. What they're saying is that according to the rules of General Relativity there shouldn't be one.

I'm a little uncomfortable with that statement. The rules of GR only insist on extreme geometric curvature and pressure in the presence of so much mass/energy, but extreme GR curvature doesn't automatically lead us to infinitely dense objects or "points". Only if our understanding of neutrons and quarks and such is correct, and the Pauli exclusion principle does not apply, can we say with absolute certainty what GR might 'predict' in extreme mass concentration cases.

 

[MichaelMo]

I understand that quark stars are on the table in theory.
This would represent a state of matter which is intermediate between a neutron star and a black hole.
The problem with that is that no such form of matter has ever been observed,
and if it can exist, the properties of quark soup cannot be predicted.

It should be noted that neutron star material as it's presumed to exist inside of neutron stars has never been directly "observed" either, I don't see why the core couldn't even be a combo of a quark star with a neutron material around the quark star. I'll mention the Pauli exclusion principle one more time because I think it's important, as well as the fact that black holes supposedly hold a charge. How do they hold their charge?

 

[Drakkith]

I'm a little uncomfortable with that statement. The rules of GR only insist on extreme geometric curvature and pressure in the presence of so much mass/energy, but extreme GR curvature doesn't automatically lead us to infinitely dense objects or "points".

As far as I know it does.

Only if our understanding of neutrons and quarks and such is correct, and the Pauli exclusion principle does not apply, can we say with absolute certainty what GR might 'predict' in extreme mass concentration cases.

We know with near-absolute certainty what GR predicts, but we don't know with any real amount of certainty what actually happens behind the event horizon.

It should be noted that neutron star material as it's presumed to exist inside of neutron stars has never been directly "observed" either, I don't see why the core couldn't even be a combo of a quark star with a neutron material around the quark star.

It might be. From wikipedia: https://en.wikipedia.org/wiki/Neutron_star#Structure

The composition of the superdense matter in the core remains uncertain. One model describes the core as superfluid neutron-degenerate matter (mostly neutrons, with some protons and electrons). More exotic forms of matter are possible, including degenerate strange matter (containing strange quarks in addition to up and down quarks), matter containing high-energy pions and kaons in addition to neutrons,[5] or ultra-dense quark-degenerate matter.

We don't really know what might exist below the event horizon, but the Pauli exclusion principle should preclude anything from achieving infinite density.

It is unknown what happens to matter inside a black hole. The PEP wouldn't apply if the in-falling matter is converted into bosons by the immense forces. And that's assuming the PEP even continues to hold inside the black hole. For all we know, it might not.

 

[nikkkom]

I'm a little uncomfortable with that statement. The rules of GR only insist on extreme geometric curvature and pressure in the presence of so much mass/energy, but extreme GR curvature doesn't automatically lead us to infinitely dense objects or "points". Only if our understanding of neutrons and quarks and such is correct, and the Pauli exclusion principle does not apply, can we say with absolute certainty what GR might 'predict' in extreme mass concentration cases.

We do know what GR predicts. Schwarzschild solution is not at all ambiguous.

GR predicts that beyond EH, direction towards the center becomes timelike. This means that there is no way for infalling matter to avoid moving towards it, just like you can't avoid moving into tomorrow.
Moreover, GR predicts that any matter reaches the center in a finite proper time interval. (What happens next, GR can't say, since math breaks down - curvature becomes infinite, etc).

The above is what people mean when they say that "GR predicts singularity".

This, of course, does not imply that this singularity is a mathematically well-behaving object. It is not.
In my opinion, the fact that GR predicts it is a breakdown of GR. Simply put, it does not correctly describe ultra-high-energy and ultra-small-distances behavior of gravitation. In my opinion, there is a better theory which gives more sensible description.

 

[Chronos]

Whatever might be hiding inside an event horizon it almost certainly is not a neutron star for. The most massive known neutron stars to date only run about 2 solar masses and the best existing measurements yield a radius of no less than 10km. That is significantly larger than the Schwarzschild radius for a 2 solar bh - which is about 6km. Assuming 10km is some kind of low limit for the radius of any neutron star. A mass of about 3.5 solar would be necessary to achieve a Schwarzschild radius of 10km. See https://arxiv.org/abs/1505.05155, The Dense Matter Equation of State from Neutron Star Radius and Mass Measurements, for further details. This appears to pretty much rule out the mega neutron star scenario. A quark star is not yet ruled out, but would require an equation of state far beyond nucleon density. As already noted, we have no evidence to suggest any state of matter with a density exceeding that of a neutron star. Most scientists suspect the singularity is nothing more than a mathematical artifact, and nature has demonstrated great resilience in avoiding the singularity paradox when it arises in other situations. I share this suspicion, but, also suspect the way around this disaster will be surprising. The clues are probably staring us in the face - e.g., how does a point particle [electron] avoid having infinite charge density [a charge singularity]?

 

[stefan r]

how does a point particle [electron] avoid having infinite charge density [a charge singularity]?

There is an uncertainty in position and momentum.

The same uncertainty should apply to particles in black holes. Any one electron would be near the singularity give or take a bit. Same/similar to the electron's position in an atom. Black hole is a singularity because there is stellar mass packed into that small space.

 

[Drakkith]

There is an uncertainty in position and momentum.

I'm pretty sure that doesn't resolve the charge singularity.

The same uncertainty should apply to particles in black holes. Any one electron would be near the singularity give or take a bit. Same/similar to the electron's position in an atom. Black hole is a singularity because there is stellar mass packed into that small space.

That's not how a singularity in GR works. It's not simply a point in space. It's also a point in time. You can't have uncertainty when the particle's world-line literally ends at the singularity.

 

[stefan r]

That's not how a singularity in GR works. It's not simply a point in space. It's also a point in time. You can't have uncertainty when the particle's world-line literally ends at the singularity.

I thought there was a time uncertainty too. I may have misunderstood the Eintein-Bohr debate.

Also does it take forever to reach the singularity?

 

[rootone]

No it does not, an infalling something reaches the (theoretical) singularity very shortly after crossing the event horizon.
Why?, because the infalling thing is trying to go faster than light, which as we all know is banned.

 

[nikkkom]

No it does not, an infalling something reaches the (theoretical) singularity very shortly after crossing the event horizon.
Why?, because the infalling thing is trying to go faster than light, which as we all know is banned.

I think the second sentence is wrong. Where did you get it?

 

[Jason R Carrico]

Why wouldn't everything approaching the event horizon already be traveling at or near the speed of light?

 

[rootone]

Yeah. that's what I meant, as far as anyone outside can see

 

[nikkkom]

Why wouldn't everything approaching the event horizon already be traveling at or near the speed of light?

Relative to what? Velocity is relative. Superluminal velocity relative to a distant observer is not prohibited in GR. The speed of light stays constant only locally.

 

[Jason R Carrico]

You're right. So let me clarify my question.

Why wouldn't anything caught in the gravitational field of the black hole be traveling at or near the speed of light, relative to the black hole, as it crossed the event horizon?

My next question would be;

Why would any observer, from any location, measure the speed of matter caught in the gravitational field of a black hole in reference to anything other than the black hole itself?

 

[Chronos]

The reference frame of the observer is irrelevant since c is c in all reference frames. Think of the old intro SR question about 2 rockets approaching from opposite directions at .9 c wrt a ground observer. Do the ground observer and rocket passengers disagree about anything besides whose watch is right?

 

[russ_watters]

Since you guys seem bent on picking apart the question instead of correcting it and answering it, let me ask it this way and see if we can get an answer:

What is the speed a remote observer at rest wrt the black hole measures for a freely falling (from infinity or equivalent) object as it approaches the event horizon?

I would think that since the escape velocity is C at the event horizon we would see the object asymptotically approaching C as it approaches the event horizon...

...unless Relativity effects make it look slower, similar to why we see x-rays generated by infalling matter...perhaps that represents the cutoff speed?

 

[Chronos]

It just like alice watching bob fall into a BH, he never quite reaches the EH from her perspective, he just redshifts into obscurity.

 

[Jason R Carrico]

Why can I not see newer posts on this thread? I keep getting emails saying there have been newer replies but I don't see anything. Why?

 

[phinds]

Why can I not see newer posts on this thread? I keep getting emails saying there have been newer replies but I don't see anything. Why?

Could be a couple of things. First, you get notifications after the posts so if you are active on the site you may see a new post and then a bit later get an email saying that there's a new post but actually it's one you've already seen. Second, sometimes a post will be deleted but it sends out an email when posted so that can cause confusion.

The thing to do is to look at the BODY of the email and see what post you are actually being notified of.

 

[Jason R Carrico]

Why can I not see newer posts on this thread? I keep getting emails saying there have been newer replies but I don'tsee anything. Why?

Could be a couple of things. First, you get notifications after the posts so if you are active on the site you may see a new post and then a bit later get an email saying that there's a new post but actually it's one you've already seen. Second, sometimes a post will be deleted but it sends out an email when posted so that can cause confusion.

The thing to do is to look at the BODY of the email and see what post you are actually being notified of.

The above showed up in my email, but shows up nowhere when I open this thread.

 

[Jason R Carrico]

I see it now. Sorry and thanks

 

[stefan r]

Since you guys seem bent on picking apart the question instead of correcting it and answering it, let me ask it this way and see if we can get an answer:

What is the speed a remote observer at rest wrt the black hole measures for a freely falling (from infinity or equivalent) object as it approaches the event horizon?

I would think that since the escape velocity is C at the event horizon we would see the object asymptotically approaching C as it approaches the event horizon...

...unless Relativity effects make it look slower, similar to why we see x-rays generated by infalling matter...perhaps that represents the cutoff speed?

Suppose the falling object broadcasts a radio message of it's current location. The broadcast starts at one gigahertz but will shift to one megahertz, then kilohertz, hertz etc. The location message was always transmitted at one gigahertz. Now you can make two measurements of velocity. Suppose location A to location B is 2 meter. Light would be able to travel that distance in 6.7 x 10^-9 seconds which is also 6.7 cycles at 1 gigahertz. The distant observer who gets a 1 hertz signal will also observe 6.7 cycles but that will take 6.7 seconds. So the distant observer is seeing the messenger drop into the hole at 0.15 meters per second while the messenger is claiming 150,000,000.
The example is not exactly correct for a drop from infinity. Also the signal and velocity would not be linear from point A to point B.

 

[Drakkith]

Why can I not see newer posts on this thread? I keep getting emails saying there have been newer replies but I don't see anything. Why?

Second, sometimes a post will be deleted but it sends out an email when posted so that can cause confusion.

Phinds is correct. I had to delete multiple posts from this thread.

Suppose the falling object broadcasts a radio message of it's current location. The broadcast starts at one gigahertz but will shift to one megahertz, then kilohertz, hertz etc. The location message was always transmitted at one gigahertz. Now you can make two measurements of velocity. Suppose location A to location B is 2 meter. Light would be able to travel that distance in 6.7 x 10^-9 seconds which is also 6.7 cycles at 1 gigahertz. The distant observer who gets a 1 hertz signal will also observe 6.7 cycles but that will take 6.7 seconds. So the distant observer is seeing the messenger drop into the hole at 0.15 meters per second while the messenger is claiming 150,000,000.
The example is not exactly correct for a drop from infinity. Also the signal and velocity would not be linear from point A to point B.

Hmmm. You sure about this? It doesn't sound right to me, but I confess I'm not sure how to do the math.

 

[stefan r]

Hmmm. You sure about this? It doesn't sound right to me, but I confess I'm not sure how to do the math.

No. Not sure of anything. I have not personally made any observations of black holes. The world looks fairly Newtonian in my house.

Also sure that a linear measurement will be wrong. Just trying to describe time dilation. Most descriptions use the word "clock". I am using a radio broadcast frequency as a "clock".

 

[phinds]

Light would be able to travel that distance in 6.7 x 10^-9

Uh ... really? And where exactly is this happening? How close are A and B to the BH?

No. Not sure of anything. I have not personally made any observations of black holes. The world looks fairly Newtonian in my house.

Also sure that a linear measurement will be wrong. Just trying to describe time dilation. Most descriptions use the word "clock". I am using a radio broadcast frequency as a "clock".

It would be helpful if you would draw a diagram of exactly what you are describing. It sounds wrong to me also but I may be misinterpreting what you are describing.

 

[stefan r]

Uh ... really? And where exactly is this happening? How close are A and B to the BH?

speed of light 299,792,458 meters per second in a vacuum.

It would be helpful if you would draw a diagram of exactly what you are describing. It sounds wrong to me also but I may be misinterpreting what you are describing.

Isaac Newton and the royal society did not think of it.
My example is crap because the signal would dilate from both gravity and also doplar effect. For stationary objects:

For a solar mass black hole the Schwarzschild radius is 2950 meters. To get a time dilation of 1 billion, 10^-9 you need √10^-18. So the transmitter is around 3 femtometers from the event horizon. Not a very good example.

Suppose it is broadcasting from 29,500 meters (r_s x 10) outside a solar mass black hole or neutron star. The time dilation is 0.949. So a radio station broadcasting at 105.1 FM will show up as 99.7FM to someone listening from far away.

 

[Drakkith]

Suppose it is broadcasting from 29,500 meters (rs x 10) outside a solar mass black hole or neutron star. The time dilation is 0.949. So a radio station broadcasting at 105.1 FM will show up as 99.7FM to someone listening from far away.

That looks correct to me. My earlier confusion was mostly from your description of the motion of the transmitter.

 

[Ken G]

I really don't see how the presence or absence of a singularity has anything to do with answering any of those questions, I'm sorry. Also, it does not relate to the presence of the "gap" in stable density, as that does not have to do with black holes at all. Whether or not an event horizon forms relates to what happens after the object has already formed, so is just not relevant to those questions. Also, one must be careful not to mistake the infinity in an arbitrary (Schwarzschild-like) time coordinate with the final state of formation of an actual object, as that final state should be in the object's own proper time.