Neutron Star to Black Hole

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The point here is the professors that have given short statements, are not familiar with the carryings on and the porky pies and misinformation, and misinterpretations that in reality can only be viewed as deliberate stalling/confusing tactics, as his questions have all been answered many times, yet he continues to argue along the same lines.
The above post, plus the preceeding posts, give examples of that.

 

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This statement again highlights the misconceptions of what Rajesh thinks is being said.....
Nether professor's posts invalidate what I have been claiming from day one.....
.
"I think the two sides (Rajesh, Paddoboy) are implicitly using the term `singularity' in
different ways. The term is a well-defined notion in classical
general relativity and therefore does not refer to the Planck/quantum
scale. But perhaps the other side thinks of the singularity as a place
where, in the real world, classical general relativity fails. This would
happen once the curvature becomes Planck scale (much before the classical
singularity where it is infinite)".

Note "where, in the real world, classical general relativity fails. This would happen once the curvature becomes Planck scale (much before the classical singularity where it is infinite)"

 

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Note where the professor says "where in the real world general relativity fails" and where he continues on and says "This would happen once the curvature becomes Planck scale" [you can also put quantum scale there if you wish] and then finishes with "(much before the classical singularity where it is infinite)"

 

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Enjoy the weekend sonny !! At least on the weekends you have the liberty to see what you like to see...

 

I see it as it is, without any baggage or agenda. That throughout at least two threads, has been your problem.

 

Q1. In general the Rotational Kinetic Energy of the Neutron Star is of the order of 10^40 Ergs. So in case Schwarzschild BH is formed due to accretion of mass by Neutron Star, then what happen to this Rotational Kinetic Energy ?

It becomes mass-energy. Note that the "coordinate" speed of light at the event horizon is zero, and nothing can move faster than light. So somewhat counterintuitively, the rotation of the collapsing star doesn't keep on increasing. In similar counterintuitive fashion, the speed of an upward photon increases. We had an interesting conversation about this kind of thing in this thread.

Q2. In case of Kerr BH which is rotating type, what rotates? The mass is at singularity, Ergosphere also cannot be stated to have this energy or mass, then what rotates ? For clarity the mass/energy here is the original BH formation mass/energy...not what is acquired due to accretion.

Nothing rotates. The Kerr black hole is bad science borne from a misunderstanding of general relativity.

Q3. What do we really mean by non rotating Schwarzschild BH or Rotating Kerr BH, when the inside of EH itself is not interacting with Physical World.

The non-rotating Schwarzschild balck hole is the frozen-star black hole as originally described by Oppenheimer. This makes perfect sense. Black holes which feature central point-singularities don't. Especially when they are said to be rotating at close our local speed of light, at a location where the local speed of light is zero.

 

Farsight, your answers above are all pseudoscience. You really do need to get a grip on the difference between what you imagine and reality. The falsehood of your answers has been delt with repeatedly. Do you really believe that if you continue saying it long enough everyone else will begin to agree?

To all others reading this, Farsight's comments have very little in common with science and/or reality.

 

Not true. If it was true, you'd be able to give a link to somewhere where something I'd said was shown to be mistaken. But you can't. However in my previous post I gave a link to a thread where Professor Tom Moore said this:

"An observer using such a coordinate system will find that the light flash will move *slower* than c close to the planet's surface than it does at infinity... As the planet's mass approaches the black hole limit, the signal emitted from the surface will seem to move more and more slowly away from the surface (and will also be seen to be increasingly red-shifted as observed from infinity). When the surface of the planet coincides with the black hole's event horizon, the signal will stop moving outward from the surface (and the redshift observed at infinity will go to infinity). So light no longer escapes..."

The light doesn't escape out because it's stopped. If it wasn't stopped, it would get out, and it wouldn't be a black hole. And nothing can move faster than light. So nothing is rotating. Also note what Quarkhead and PhysBang conceded about spacetime here and here. Spacetime is static. There's no motion in it. Light doesn't move through it, because it's an abstract mathematical model. Light moves through space. It's space around a black hole, not spacetime. And that space is not rotating faster than the local speed of light. Which is zero.

Rajesh: best ignore OnlyMe. His physics knowledge is at the popscience level, and he is dogmatic in his refusal to follow up references to serious physics.

 

Very good response, especially with respect to that last paragraph, which sums up the problem in most of these discussions... We get trapped between theory and some attempt to put it, into some real context... That leads to speculations about what physically lies within the event horizon, a subject for QM and quantum gravity, not yet resolved.

 

Do,you actually read, Farsight? see the emphasis on the word "seem", in Prof. Moore's comment?

The full quote of Prof. Moore's comment.., and you Farsight should pay special attention to the first and last sentences emphasized in red, since in this case Prof. Moore's response was to a comment of yours.....

Prof. Moore:

This is a good example of how intuitive models can go astray.

The argument presumes that the light signal does not "slow down," but what exactly does that mean? An observer at rest relative to the star will always measure the outgoing light signal to have speed c *locally,* (that is, as the flash passes through a laboratory that is very small compared to scale over which spacetime is locally curved), but to talk about the speed of a signal emerging from the planet's surface and going all the way to infinity, one needs a *global* coordinate system (one that applies at all positions in spacetime, such as the Schwarzschild coordinate system) to talk about the signal's speed at various points. An observer using such a coordinate system will find that the light flash will move *slower* than c close to the planet's surface than it does at at infinity. This does not contradict the previous results, because time runs more slowly for observers close to the planet's surface than for those higher up, so what looks like something moving with speed c to an observer close to the surface looks like something moving slower to someone whose clock is running faster.

As the planet's mass approaches the black hole limit, the signal emitted from the surface will seem to move more and more slowly away from the surface (and will also be seen to be increasingly red-shifted as observed from infinity). When the surface of the planet coincides with the black hole's event horizon, the signal will stop moving outward from the surface (and the redshift observed at infinity will go to infinity). So light no longer escapes.

This also does not contradict the statement about an observer at rest on the surface seeing the signal to have speed c, because as event horizon moves beyond the planet's surface, that surface can no longer remain at rest, but in fact must go to r = 0 in a finite time (as measured by an observer on the surface), just as surely as the past must go towards the future. Even then, an observer on the surface will *still* see the light moving outward at speed c, but from the perspective of the global coordinate system, it is simply that the observer is falling faster toward r = 0 than the signal is.

To understand all this fully, I strongly recommend that the questioner take a course in general relativity!

Best wishes, Tom M.​

Do you ever stop the cherry picking? It is only from a global frame of reference, which is the same as saying as seen by a distant observer that light seems to stop.

 

Nice reply from Professor Moore. And really to see the denigration of this thread, further then it already has with Farsight's fairy tale like comments is sad.
The relevant part of Professor Moore's statement is the following......
"Therefore, the properties of the Kerr black hole that everyone talks about are properties of the spacetime (that is, the gravitational field), not the singularity. When you extract angular momentum from a Kerr black hole, you are extracting it from the *field*, not the singularity. The singularity is simply where worldlines go to die".
This is a similar reason how gravity itself "gets out" of a BH. It's a fossil field, a field [spacetime] that exists from the star that collapsed to form the BH.

Just to correct Farsight's "great error" Light is never seen to stop, in any FoR, ever! It does get redshifted beyond viewable range to gradually fade from view.
From any local frame, all light crosses the EH to oblivion except for those photons that are emitted directly radially away. These will seem to "hover" forever just above the EH, analogous to a fish swimming upstream at 10kms/hr, against a current of 10kms/hr.
But that is moving away again from what this thread is about.

In essence it is logical to say the Singularity is evident from where the current laws and GR fail. Again in essence, most physicists don't believe that the classical definition of a singularity [the point singularity] does not really exist.
Although I must add, as professor Moore has said, we are not able to verify observationally, any effect inside the EH proper of any BH, a well known trait and the defining scenario of a BH. But if that BH was a Kerr metric, with an ergosphere [frame dragging] we can see and verify and extract theoretically energy from that region.

 

It is not good to jump into the concept of the fossil field .... It again assumes that the GR solution, which includes a point singularity is correct, rather than theoretical.., and that once the graviationnal field is first established, it retains an angular momentum and inertia equivalent to the originating massive object. ???

If you could explain how the fossil field could exist without any central massive object and how it could have an angular momentum equal to the original mass, in this case the colapsing black hole..., there would be no need to explore any rendition of quantum gravity.

Black holes seem to grow or gain mass over time. That does not seem even possible for a fossil field.

Both Kerr and Schwartzchild black holes, assume a point singularity and describe only the gravitational field.., inside and outside of the event horizon.

 

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Hmmm
The gravity of any BH is the gravity that was there before the BH formed.
I don't see it as having anything to do with any QGT
Gravity is a property of spacetime, in the presence of mass.
It's there, before the BH was ever formed.
http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_gravity.html

 

Your reference begins,

Purely in terms of general relativity, there is no problem here.​

Now think back to some of the earlier comments, Tasha has obtained... The theory assumes a point singularity, which is not generally accepted as existing in reality.

Paddoboy, the concept of fossil fields raises more issues than it solves. Especially when its biggest contribution is that it eliminates issues that are introduced by assuming a point singularity exists. Or speed of light issues that are generated by assuming that the field crosses the event horizon... Both the Kerr and Schwartzchild solutions describe the field all the way to the singularity...

Like I have said at other times, part of the problem is that the discussion involves attempts to treat theory as reality. In another discussion you might find an argument that describes how a gravitational field dissipates at its propagation speed, the speed of light, when the central mass is mysteriously removed. Or if the idea of a fossil field as a real field were accurate, as a massive object creating a gravitational field moves, which as far as we can tell they all do, they would leave a fully functional fossil field trail in their wake.

 

I don't see it that way. Even if a point singularity did exist, what has that to do with the fossil field that was there in the first place before the BH even formed.
I fail to see the connection you are making.
I also think saying the field crosses the horizon is misleading...the field is the horizon, both inside and outside...it is spacetime...it is gravity [with the help of mass]

I know what a scientific theory is.....I know that they are "best estimates" based on current knowledge....I also know that some theories like GR/SR grow in stature and certainty the more successful they continue to be...I know that even accepting the near certainty of GR, that that certainty still is only evident within its accepted parameters.
We also in earth based situations and non relativistic scenarios including space endeavours still use Newtonian concepts as "reality"
Yes, we sometimes infer reality to incumbent theories that have stood the test of time.

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Let me have a go. If the mass/Singularity were magically removed from a BH, since all paths were leading to that singularity/mass, it would be impossible for any signal to head the other way and inform the fossil field that it, the mass/singularity was gone. This is theoretically based on the non-linearity of gravity/spacetime.
"A massless black hole which is a stable topological structure held together by the nonlinearity of its gravitational field".
http://scienceworld.wolfram.com/physics/EternalBlackHole.html


Your second inference doesn't make sense. Unless I'm misunderstanding something you are trying to say.
A gravitational field, any gravitational field, exhibits itself in the presence of mass, along with mass, and follows mass, much as rolling a bowling ball across a trampoline.
You seem to me to somehow be trying to differentiate a gravity field from a mass, from a fossil gravity field left by a former star that still has the mass, albeit in a more condensed form
The following link discusses gravity and gravitons.
http://www.astronomycafe.net/qadir/q756.html

 

Paddoboy, from Tasha's post #129 — Prof. Moore describes the theoretical case and then in the last paragraph and that portion emphasized in bold by myself, speaks to the issue that involves QM and QG.

Dear Tashja,

The Kerr spacetime is a *vacuum* solution to the Einstein field equation that has the right properties for describing the gravitational field outside a spinning compact object. It describes the spacetime in the vacuum outside an uncollapsed object (e.g. the earth) as well as black holes. In the former case, the constants a and M in the Kerr metric equation (spin per unit mass and mass respectively) are determined by connecting the solution to the Einstein equation inside the spinning object to the Kerr spacetime outside the object, by matching across the boundary represented by the object's surface.

In the case of a black hole, we cannot determine the spacetime inside the singularity in order to do this matching across the boundary. Presumably, however, the Kerr metric's values of a (angular momentum per unit mass) and M (mass-energy) will be conserved as the original source falls into the singularity. But the point is that in GR the singularity is simply a singular mathematical point in the vacuum solution that now applies everywhere *else.* We can no longer talk meaningfully about the singularity's spin or even its mass. We can only talk about (or measure) what we observe imprinted in the gravitational field. The physics of the field outside the Kerr black hole's event horizon (which is the only thing that we can possibly observe from an outside perspective) is completely disconnected from the singularity.

Therefore, the properties of the Kerr black hole that everyone talks about are properties of the spacetime (that is, the gravitational field), not the singularity. When you extract angular momentum from a Kerr black hole, you are extracting it from the *field*, not the singularity. The singularity is simply where worldlines go to die.

Of course, in some future quantum theory of gravitation, the classical singularity will probably not be a mathematical point, but be "smeared out" in some sense yet to be defined. In such a theory, one might be able to connect the vacuum spacetime to the spacetime inside the source through matching in a similar sense to what one can do with extended objects. Then maybe we can talk about the properties of the source and how it is connected to the properties of the Kerr spacetime in the vacuum around it. But this will not change the fact that we can "mine" the Kerr spacetime for *its* angular momentum and *its* energy. In absence of a quantum theory of gravitation, we cannot say anything about how this mining affects the source.

Hope that helps,

Tom M.​

If you limit the discussion to an entirely theoretical context and in that to a discussion of black holes as described solely within the context of GR, you are dealing with a point singularity and spacetime and describing the gravitational field. In that theoretical context you are talking only about the spacetime that exists outside the event horizon, as it affects reality, though the theory extends to the singularity, nothing inside the event horizon can be observed and is theoretically separated from spacetime outside the event horizon. That is as described in more than one solution of EFE.

When you read carefully that last paragraph, Prof. Moore suggests that some future model of quantum gravity may connect the spacetime inside the event horizon with that outside.., and in doing so (my words) the physical mass of the black hole with spacetime as a whole. If it were not the case that reason suggests, that a gravitational field cannot be sustained without the presence of mass, there would be no need to search for any model of quantum gravity.., physics would have already solved the problems and complications associated with the event horizon, as suggested by both Schwartschaild and Kerr solutions......, and we could just say that a gravitational field is associated with the presence of mass..., except in the case of black holes..., where no mass is needed because the field sustains itself!

This could go on and on. The concept of fossil fieldspresents more problems than it offers solutions.

That last sentence

In absence of a quantum theory of gravitation, we cannot say anything about how this mining affects the source. (Prof. Moore)​

implies that there is a currently unknown connection between the mass of a black hole and the observable gravitatinal field, not described by GR.., which may be described by some future model of QG.

 

Except of course it is the same gravitational field/spacetime.
There is no disconnection....They are glued for want of a different word.
I seriously cannot see the difficulty you see in a fossil field.

 

So is this gravitation , field/spacetime , geometry , or a real thing ?

 

Our only problem is we do not have a validated model to describe that same spacetime/gravitational field......But it is the same gravitational field/spacetime, as what exists and makes up the BH proper, the EH, the ergosphere if Kerr metric, and beyond.