"Inner Horizon" of a Black Hole??

[thylacine]

I was watching a tape of a Nova program on Black Holes (from Oct 2006). About 27 minutes in they talk about the "Inner Horizon" of a Black Hole. What is this exactly?

BTW they were not talking about a rotating Black Hole, nor was it something at the Planck scale AFAICT.

They are talking about falling into such a large Black Hole that you can experience it for some time after passing through the event horizon. Then they say:

NARRATOR: ... Deep within, there's an inner horizon; a logjam of trapped light and energy.

PHYSICIST: At a certain moment, as we hit the inner horizon, there's this infinitely bright blinding flash. That's the stuff that's been waiting there trying to get out. It's just held there at the inner horizon.

Does anyone know what exactly this "Inner Horizon" of a Black Hole is? Informed speculation welcome.

[jamzfive]

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Informed speculation welcome.

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Informed speculation: The inner horizon is the actual surface of the black hole? As opposed to the event horizon, which is the area above the surface which denotes where gravity becomes too strong for anything to escape. I.e., the inner horizon is something you could actually stand on (disregarding what the effects of gravity on you would be), and the event horizon could be thought of as an atmosphere.

maybe?

jb

[pokerbobo]

I would agree. The inner horizon sounds like the mass of the black hole, and the event horizon would expand based on the density of the mass.

[jamzfive]

meh... turns out I'm wrong. Just google it.

jb

[Metric]

Never heard this used as a technical term. The term "event horizon" has a well-known meaning, but this might be colloquial usage. There are boundaries of other spacetime regions that have interesting properties, e.g. in the case of rotating black holes, etc. but I don't usually hear those referred to as horizons.

[thylacine]

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Never heard this used as a technical term. The term "event horizon" has a well-known meaning, but this might be colloquial usage. There are boundaries of other spacetime regions that have interesting properties, e.g. in the case of rotating black holes, etc. but I don't usually hear those referred to as horizons.

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The physicist in the quote is Andrew Hamilton from University of Colorado. They were definitely talking about this "Inner Horizon" as something you would encounter later after having already passed through the event horizon.

[thylacine]

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[ QUOTE ]
Never heard this used as a technical term. The term "event horizon" has a well-known meaning, but this might be colloquial usage. There are boundaries of other spacetime regions that have interesting properties, e.g. in the case of rotating black holes, etc. but I don't usually hear those referred to as horizons.

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The physicist in the quote is Andrew Hamilton from University of Colorado. They were definitely talking about this "Inner Horizon" as something you would encounter later after having already passed through the event horizon.

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Okay, I just googled "Nova Inner Horizon of a Black Hole Andrew Hamilton from University of Colorado" and here are a couple of links


http://www.nasa.gov/vision/universe/..._roadshow.html

http://www.pbs.org/wgbh/nova/transcr..._blackhol.html

[Metric]

Googled "inner horizon" and found it used quite a bit in the context of Reissner-Nordstrom (electrically charged) black holes, which I have apparently neglected in my studies. The structure is somewhat more complicated than standard Schwarzschild black holes. E.G.

http://staff.science.uva.nl/~jpschaar/report/node7.html

"It turns out that the presence of the inner horizon introduces some very different features w.r.t. the Schwarzschild solution. One of the most important, from an infalling observer point of view, is the fact that the curvature singularity is timelike now, which means it can be avoided and even better; free falling observers cannot reach it. At first it was believed that this opens up the possibility to avoid ending up at the curvature singularity in the Schwarzschild space-time just by bringing a charge with you. The idea was that when you fall in the Schwarzschild black hole, it becomes charged and turns into a Reissner-Nordstrøm black hole. Sadly enough, this will probably not work, because from perturbation calculations it is suspected that slightly non-spherical collapse will turn the inner horizon into a singularity.

The outer horizon in this space-time behaves just as the event-horizon in the Schwarzschild case. When inside r+ you are forced to reach r-, just as an infalling observer in Schwarzschild is forced to reach the curvature singularity. When crossing the inner horizon the observer would be face to face with a curvature singularity, but as mentioned before an observer will not end up at the singularity. Instead of ending up at the singularity, the observer can continue into another asymptotically flat spacetime. (If it would be the same asymptotically flat space-time the causal structure would not be uniquely defined, it would depend on whether you came from the region inside r- or from outside r+). When all timelike curves can be extended to infinity (they never end up at a singularity), as is the case, the space-time is called (time-like) geodesically complete."

[HP]

hey why we're on the topic, can you have a 'naked singularity'? I remember reading about it in some book

like, if the black hole was rotating fast enough, and say it had enough positive charge, then could an electron wiz past the very centre of the black hole?

black holes rule

[Metric]

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hey why we're on the topic, can you have a 'naked singularity'? I remember reading about it in some book

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It has not been established as a fact of nature, but the "cosmic censorship hypothesis" is basically that there are no naked singularities -- they are all clothed with an event horizon.