A black hole is not a solid object in the same way that a neutron star is.
I guess we (incorrectly?) associate the event horizon as being the black hole when perhaps we should think of a point at the centre as the black hole.
GR doesn't gives a God's Eye view alas. It only relates information & measurement from different/separated viewpoints in time and/or space. Thus a hard core relativist could claim that your question has no meaning. But we must attempt try to connect the rigor of GR to everyday intuition. Plus I'm not hard core. :-)
Consider the centre of our galaxy. There is an object there which contains the mass of many million Suns within a small zone. Knowing that a black hole's radius is 3km per solar mass ( Schwarzschild ) then that is a mere few millions of kilometers in diameter. Hardly even out to the orbit of Mercury. This galactic centre object was deduced to be so by the patient observation of the orbits of stars going around it. Ordinary Kepler's laws were used to come up with the mass. So provided you stay a long way away it really doesn't matter much if it is a black hole, an exotic spider, or a giant bucket of fudge cake. Newton's laws will do fine for examining from that distance. Just use the total mass at such and such location. The geometric centre as perceived distantly will do fine.
Of course it isn't fudge cake. But the extremata of relativistic effects can only be gleaned close up, or if something ventures close up and/or gravitational waves happen. Unlike the movies the event horizon doesn't look like anything when you come up close to it. It's not like some shiny surface or anything. You would not notice any particular signal when you cross to within the radius. Well, not immediately at least. Later on you would die by various means.
What would happen is that as an observer progressively nears they discover that they can't see things normally. The appearance of things that were seen as straight becomes bendy and when they look back outwards to the universe they came from : everything is sped up. One could have a close shave with a black hole ( an ultra high performance rocket required here ), scoot down close to the horizon and when you come back after maybe some hours of ship time find the rest of the universe is a million years older.
{ Actually the movie Interstellar had that part right. The guy stays in the main ship while the others go down to a planet nearby a black hole. A mere few hours by their reckoning. They get slammed by a tidal wave etc. On returning the ship board guy is 20+ years older. The plot weakness here I think is why the guy didn't go crazy after several decades alone, but no one is asking me. }
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
There does remain the issue of what is actually at the centre of the hole, beneath the event horizon. GR predicts a singularity at the centre. This is mathematics speak for some quantity becoming infinite at a precise point. Singularities are of two basic types in GR.
- the simpler is where the infinity goes away by a different choice of co-ordinate system. The event horizon is like that. A distant observer sees a surface where a time rate/ratio goes to zero, or infinity if you invert it. By swapping to an observer that descends across that special radius the infinity goes away. But it is still a sort of infinity as you will never see the remainder of the Universe again ! :-(
- the central singularity can't be transformed away by choice of viewpoint. All observers within the horizon will agree on the reality of it. All will be crushed when they reach it regardless. Abandon hope all ye ....
This gives rise to a few schools of thought about the centre :
- who cares ? We'll never measure it anyway. Move on, nothing to see here.
- if it is infinite density then so what ? Too bad, so sad. We humans may have too much pretense about what can and can't be thought of as 'logical'. The restraint is our own imagination, thought processes, or whatever and not reality. Infinity can be cool.
- some have tried to 'rescue' GR from this singularity 'problem'. Most are a version that mixes GR with quantum mechanics.
By and large QM avoids classical mathematical singularities by not allowing infinite densities ( energy or matter ). Things will always wiggle out before that happens. Mr Heisenberg helps here by structuring the theory to not allow simultaneous exact measurement, nay existence, of certain pairs of quantities that could enjoin in some ratio that works out as infinite. Nice move Werner. This approach has famously worked for all the non-gravitational forces. For instance it explains why atoms exist with some spatial extent : you can't have everything sitting on top of each other in the middle. However such forces assume at least Special Relativity ( no gravity about ) as the baseline reality for the various quantum fields to exist within. Spacetime is the substrate assumed to be there for whatever reason. The fields are layered on top of that assumption.
With GR spacetime is the substrate. This is a game changer for theorists. How does one create quanta, or pieces of, spacetime that follow the ( weirdo ) rules of quantum mechanics ? No one has got that right, yet. Not the least problem is how to think about it ! In any event if there is a smallest possible 'hypercube' of spacetime then you can only stuff so much into it. Heisenberg won't let an endless amount into that 'quantum volume'. It might be a humungous number, but that's still finite.
Cheers, Mike.
( edit ) BTW : these little hypercubes would have to be epically tiny. Maybe say 10100 of them per litre per second of spacetime. Should one really worry about that level of detail ? Plus larger slabs of spacetime have to emerge as a probable outcome of mixing many alternative schemes of interconnects b/w the quanta. If you don't find that offensively anti-intuitive then I don't what would be ! :-))
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
What influence on the merging process do have the very, very strong magnetic fields of the neutronstars. Off course the momentum of inertia are also tremendously high, but electromagnetic forces are the strongest in our world. This is one parameter more to be attended in modelling. I never read any bout this. Why not?
Is the conjunstion of this magnetic fields the reason for the gamma ray peak?
Kind regards and happy crunching
Martin
By the way: That we do not know any about pulsar action of one of them is not at all an indication for missing magnetic fields.
To my knowledge no one has a decent clue regarding the mechanism of pulsar beaming. While there is a massive amount of energy in those magnetic fields, it will always be dwarfed ( via mc2 ) by the gravitational component. The best estimate for the average density of neutron star material is three times nuclear density. That means the neutrons are packed in harder than everyday matter. I guess the photon ( EM field ) density is minor in comparison. Another way of putting this is that gravity always adds ( no negative masses ) while EM forces can and do cancel by charge movement.
Bear in mind that this collision - and the hope of many to come - are immensely valuable sources of data for the theorists to answer such questions. They will be re-modelling .... :-)
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
To be exact it is the accretion disk of inspiralling material that responsible for the magnetic field, this would be present even if the central object was not a black hole. The innermost material has to lose energy in order to fall inwards, and one model has magnetic interactions that transfer angular momentum from the innermost orbits to the outer ones.
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
An extra thought : Stephen Hawking made much of the idea that with a sufficiently strong gravitational gradient then EM quanta may appear. A 'vacuum fluctuation' as it were. This is the basis for his hypothesis of radiation generation just outside of the horizon, with maybe particle/anti-particle pairs such that one goes into the hole and the other escapes. Hence over extraordinary time intervals black holes may 'evaporate' with said loss of mass/energy.
Now if that's true of an undisturbed black hole, how much would this process come into play in the violence of collisions with extreme density objects ? Just sayin ....
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
So what I get from that is
)
So what I get from those infos is that black holes are too symmetric to emit any sort of *continuous* gravitational wave. Thanks for that.
Mike Hewson wrote:A black
)
I guess we (incorrectly?) associate the event horizon as being the black hole when perhaps we should think of a point at the centre as the black hole.
AgentB wrote:Mike Hewson
)
GR doesn't gives a God's Eye view alas. It only relates information & measurement from different/separated viewpoints in time and/or space. Thus a hard core relativist could claim that your question has no meaning. But we must attempt try to connect the rigor of GR to everyday intuition. Plus I'm not hard core. :-)
Consider the centre of our galaxy. There is an object there which contains the mass of many million Suns within a small zone. Knowing that a black hole's radius is 3km per solar mass ( Schwarzschild ) then that is a mere few millions of kilometers in diameter. Hardly even out to the orbit of Mercury. This galactic centre object was deduced to be so by the patient observation of the orbits of stars going around it. Ordinary Kepler's laws were used to come up with the mass. So provided you stay a long way away it really doesn't matter much if it is a black hole, an exotic spider, or a giant bucket of fudge cake. Newton's laws will do fine for examining from that distance. Just use the total mass at such and such location. The geometric centre as perceived distantly will do fine.
Of course it isn't fudge cake. But the extremata of relativistic effects can only be gleaned close up, or if something ventures close up and/or gravitational waves happen. Unlike the movies the event horizon doesn't look like anything when you come up close to it. It's not like some shiny surface or anything. You would not notice any particular signal when you cross to within the radius. Well, not immediately at least. Later on you would die by various means.
What would happen is that as an observer progressively nears they discover that they can't see things normally. The appearance of things that were seen as straight becomes bendy and when they look back outwards to the universe they came from : everything is sped up. One could have a close shave with a black hole ( an ultra high performance rocket required here ), scoot down close to the horizon and when you come back after maybe some hours of ship time find the rest of the universe is a million years older.
{ Actually the movie Interstellar had that part right. The guy stays in the main ship while the others go down to a planet nearby a black hole. A mere few hours by their reckoning. They get slammed by a tidal wave etc. On returning the ship board guy is 20+ years older. The plot weakness here I think is why the guy didn't go crazy after several decades alone, but no one is asking me. }
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
There does remain the issue
)
There does remain the issue of what is actually at the centre of the hole, beneath the event horizon. GR predicts a singularity at the centre. This is mathematics speak for some quantity becoming infinite at a precise point. Singularities are of two basic types in GR.
- the simpler is where the infinity goes away by a different choice of co-ordinate system. The event horizon is like that. A distant observer sees a surface where a time rate/ratio goes to zero, or infinity if you invert it. By swapping to an observer that descends across that special radius the infinity goes away. But it is still a sort of infinity as you will never see the remainder of the Universe again ! :-(
- the central singularity can't be transformed away by choice of viewpoint. All observers within the horizon will agree on the reality of it. All will be crushed when they reach it regardless. Abandon hope all ye ....
This gives rise to a few schools of thought about the centre :
- who cares ? We'll never measure it anyway. Move on, nothing to see here.
- if it is infinite density then so what ? Too bad, so sad. We humans may have too much pretense about what can and can't be thought of as 'logical'. The restraint is our own imagination, thought processes, or whatever and not reality. Infinity can be cool.
- some have tried to 'rescue' GR from this singularity 'problem'. Most are a version that mixes GR with quantum mechanics.
By and large QM avoids classical mathematical singularities by not allowing infinite densities ( energy or matter ). Things will always wiggle out before that happens. Mr Heisenberg helps here by structuring the theory to not allow simultaneous exact measurement, nay existence, of certain pairs of quantities that could enjoin in some ratio that works out as infinite. Nice move Werner. This approach has famously worked for all the non-gravitational forces. For instance it explains why atoms exist with some spatial extent : you can't have everything sitting on top of each other in the middle. However such forces assume at least Special Relativity ( no gravity about ) as the baseline reality for the various quantum fields to exist within. Spacetime is the substrate assumed to be there for whatever reason. The fields are layered on top of that assumption.
With GR spacetime is the substrate. This is a game changer for theorists. How does one create quanta, or pieces of, spacetime that follow the ( weirdo ) rules of quantum mechanics ? No one has got that right, yet. Not the least problem is how to think about it ! In any event if there is a smallest possible 'hypercube' of spacetime then you can only stuff so much into it. Heisenberg won't let an endless amount into that 'quantum volume'. It might be a humungous number, but that's still finite.
Cheers, Mike.
( edit ) BTW : these little hypercubes would have to be epically tiny. Maybe say 10100 of them per litre per second of spacetime. Should one really worry about that level of detail ? Plus larger slabs of spacetime have to emerge as a probable outcome of mixing many alternative schemes of interconnects b/w the quanta. If you don't find that offensively anti-intuitive then I don't what would be ! :-))
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
Mike Hewson wrote:Move on,
)
Hummm, good one, that.
Hallo!What influence on the
)
Hallo!
What influence on the merging process do have the very, very strong magnetic fields of the neutronstars. Off course the momentum of inertia are also tremendously high, but electromagnetic forces are the strongest in our world. This is one parameter more to be attended in modelling. I never read any bout this. Why not?
Is the conjunstion of this magnetic fields the reason for the gamma ray peak?
Kind regards and happy crunching
Martin
By the way: That we do not know any about pulsar action of one of them is not at all an indication for missing magnetic fields.
astro-marwil wrote:What
)
An outstanding question. Black holes can have magnetic fields too.
http://www.sciencealert.com/the-magnetic-field-just-outside-our-black-hole-has-been-studied-for-the-first-time
Might they release some observable energy upon merger?
To my knowledge no one has a
)
To my knowledge no one has a decent clue regarding the mechanism of pulsar beaming. While there is a massive amount of energy in those magnetic fields, it will always be dwarfed ( via mc2 ) by the gravitational component. The best estimate for the average density of neutron star material is three times nuclear density. That means the neutrons are packed in harder than everyday matter. I guess the photon ( EM field ) density is minor in comparison. Another way of putting this is that gravity always adds ( no negative masses ) while EM forces can and do cancel by charge movement.
Bear in mind that this collision - and the hope of many to come - are immensely valuable sources of data for the theorists to answer such questions. They will be re-modelling .... :-)
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
To be exact it is the
)
To be exact it is the accretion disk of inspiralling material that responsible for the magnetic field, this would be present even if the central object was not a black hole. The innermost material has to lose energy in order to fall inwards, and one model has magnetic interactions that transfer angular momentum from the innermost orbits to the outer ones.
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
An extra thought : Stephen
)
An extra thought : Stephen Hawking made much of the idea that with a sufficiently strong gravitational gradient then EM quanta may appear. A 'vacuum fluctuation' as it were. This is the basis for his hypothesis of radiation generation just outside of the horizon, with maybe particle/anti-particle pairs such that one goes into the hole and the other escapes. Hence over extraordinary time intervals black holes may 'evaporate' with said loss of mass/energy.
Now if that's true of an undisturbed black hole, how much would this process come into play in the violence of collisions with extreme density objects ? Just sayin ....
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal