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Author Topic: Can a body of mass have a stable orbit inside the event horizon of a black hole.  (Read 2807 times)

Offline bizerl

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I swear, this forum needs a dedicated black hole section!

This occurred to me when it was mentioned that one can pass the event horizon with no ill effects, provided the black hole was massive enough. Could something find itself forever trapped in orbit inside the event horizon of a black hole or would it just get sucked straight down into the centre?


 

Offline Supercryptid

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As far as I am aware, no stable orbits can exist inside of the event horizon. There is a region just outside of the event horizon (called the photon sphere) where the closest stable orbit can exist. This is about 50% larger than the diameter of the event horizon itself. It is at this point where objects travelling at the speed of light (i.e. photons) can enter a stable orbit. Any closer than that, and you'd have to exceed the speed of light to keep your orbit. Since that isn't possible, you fall in.
 

Offline damocles

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As far as I am aware, no stable orbits can exist inside of the event horizon. There is a region just outside of the event horizon (called the photon sphere) where the closest stable orbit can exist. This is about 50% larger than the diameter of the event horizon itself. It is at this point where objects travelling at the speed of light (i.e. photons) can enter a stable orbit. Any closer than that, and you'd have to exceed the speed of light to keep your orbit. Since that isn't possible, you fall in.

It seems to me that this might lead to some really interesting effects. If a photon were to scatter off a particle of matter at the right position, then some of its wave function would be scattered in such a manner as to lock it into such an orbit. Should we expect every long-lived black hole to have orbiting photons in stable orbits?

If photons could be scattered into stable orbits, then should it also be possible for matter entering the black hole to scatter them out again?? Are black holes really white?

And finally, this interacts with another question in this forum -- if a photon is in a stable orbit around a black hole, and the length of the orbit is an integral number of wavelengths (analogue of Bohr hydrogen atom model) then its wavefunction is a stationary state. Is this a case of a stationary photon?
 

Offline Bill S

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Is this a case of a stationary photon?

If the answer to this question is "yes", we must have an odd situation.

The photon is in orbit, so it is accelerating, so we have a particle that is accelerating, maintaining a steady speed and stationary, all at the same time!

that sounds like QM to me. :)
 

Offline Soul Surfer

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Funnily the answer is no and then yes. 

The classic Schwarzschild black hole has no angular momentum and according to mathematics (not physics) it collapses to a mathematical point if infinite density and energy.

This is what all the text books talk about.  It is lazy and a total fiction on many counts and should be deleted from the record.   This fictional but often quoted solution clearly has no stable orbits.

A more physical black hole solution is the Kerr black hole, this does contain angular momentum and collapses to a ring not a point singularity so therefore it has a single stable orbit the ring singularity.

This also implies that there is a theoretical maximum amount of angular momentum that a black hole with a specific mass may contain.

However physics suggests that the production of more particles by the high energy collisions between particles during the continued collapse inside the event horizon may be able reduce the coherent angular momentum energy and effectively side step this limit but I have as yet not been able to find any references suggesting that this could happen.
 

Offline wolfekeeper

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Well, there's no stable orbits within the 'photon sphere' which is found at 1.5 times the radius of the event horizon so I can't see how there's going to be one within the event horizon either.

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

Offline Soul Surfer

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« Last Edit: 06/10/2012 19:22:06 by Soul Surfer »
 

lean bean

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Orbits around Kerr black holesÖ Iím still figuring this java program outÖ
I donít think it can do orbits within the event horizon, Iím not saying  it possible or not.
Kerr Stone program.
For those interested, download    gr Kerr stone 522kb .jar  And gr Kerr stone 115 kb .pdf for info.

http://www.compadre.org/OSP/document/ServeFile.cfm?ID=8860&DocID=1185
 

Offline wolfekeeper

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I personally don't think you can even get through the event horizon; I think that Hawking-type radiation gets more intense as you get close, and at the limit that tears you apart. The idea that you can cross the event horizon safely is based on the no-hair conjecture which completely ignores quantum mechanics.

The point with a black hole there is actually a reference frame that matters; you're moving relative to the black hole, and towards the event horizon, there's nothing stopping QM forming an impenetrable barrier there.

http://en.wikipedia.org/wiki/No-hair_theorem
http://en.wikipedia.org/wiki/Black_hole_information_paradox
 

Offline damocles

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I personally don't think you can even get through the event horizon; I think that Hawking-type radiation gets more intense as you get close, and at the limit that tears you apart. The idea that you can cross the event horizon safely is based on the no-hair conjecture which completely ignores quantum mechanics.

The point with a black hole there is actually a reference frame that matters; you're moving relative to the black hole, and towards the event horizon, there's nothing stopping QM forming an impenetrable barrier there.

http://en.wikipedia.org/wiki/No-hair_theorem
http://en.wikipedia.org/wiki/Black_hole_information_paradox

This debate is fast becoming one about the interpretation of mathematical models and/or the relative merits of competitive models. It is a pretty good example of Aristotelian philosophy; it cannot be science, because science must be based on observation, not contemplation, and observation on this question is impossible because information cannot be transmitted out of a black hole.
 

Offline wolfekeeper

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Not quite, because you can view the universe outside the black hole and determine the laws of physics and use it to make predictions about how black holes behave.

In principle we can test many theories by examining black holes that form, black holes that exist, and black holes that evaporate.
 

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