# Tag Info

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It is a misperception by (non-scientist) writers. The black hole physical model is a model based on General Relativity only. This tells something about real black holes, and have many interesting and complicated properties. Still, all scientists know that in the local conditions of very small scale and high density it is the realm of quantum mechanics, that ...

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Matter does fall in, but it's not trivial for this to happen, and the rate varies a lot between different cases. The thing is black holes don't suck matter in, just as the Sun isn't sucking in the Earth. A test particle in vacuum placed in orbit around a black hole will orbit forever. In an accretion disk, interactions between particles allow for angular ...

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A tidal force happens because different parts of the infalling object are trying to move along different geodesics. Suppose we take the 3-vector $\eta$ to be the distance between two points, then we can calculate how $\eta$ changes as the object falls inwards. If $\eta$ is constant then the distance between the points isn't changing and there is no tidal ...

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Suppose I am a long way from a black hole watching you are hovering near the event horizon, then your time is dilated with respect to mine. I won't go into the details since lots of questions hereabouts involve this calculation. I'll just mention the result: $$\frac{d\tau}{dt} = \sqrt{1 - \frac{2GM}{c^2r}} \tag{1}$$ In this equation $d\tau$ is the number ...

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It would not give the impression the universe was expanding. The expansion of the universe is related to the Ricci tensor and scalar. For a black hole of the type you describe the Ricci tensor and scalar are both zero. If you mark out any volume of space and watch it then its volume will not increase with time. However in the black hole geometry the Weyl ...

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If we consider the total angular momentum of the whole system, i.e. the Kerr black hole plus the satellite, then the total angular momentum must be conserved. So yes, any change in the angular momentum of the satellite will be matched by an equal and opposite change in the angular momentum of the black hole. This is the principle behind the Penrose process ...

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You are thinking classical physics + General Relativity. In the centre of a black hole is a gravitational singularity, a one-dimensional point which contains infinite mass in an infinitely small space, where gravity become infinite and space-time curves infinitely, and where the laws of physics as we know them cease to operate. As the eminent American ...

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I think a possible analogy would be to imagine that the singularity is a waterfall. By emitting light, you are trying to send a signal upstream using a tame fish. Outside the event horizon the fish is able to make headway against the current. But the river flows so fast within the event horizon as it approaches the waterfall, that your fish ends up going ...

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The infalling observer can 'see' whatever events are in its past light cone. The past lightcone of the infalling observer at the point of intersection with the horizon does not enclose the entire exterior region. In fact, no point on the infalling trajectory does, even at the singularity. Therefore the infalling observer unambiguously does not see the "end ...

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If you mean the black hole event horizon then the escape speed is $c$, the speed of light. This is in fact the definition of the event horizon radius, known as the Schwarzschild Radius and given by the following formula: $$R = \frac{2 G M}{c^2}$$ You can use this formula for computing escape velocities for larger radius values. Instead of the letter $c$ ...

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Now there is a light ray moving outward at the speed of light. I'm afraid that isn't the case; within the event horizon of a Schwarzschild black hole, the radial coordinate is timelike and so, moving 'outward' toward the horizon is as impossible as moving 'backward' in time. This plain to see in the Kruskal–Szekeres coordinates: Image credit See ...

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You can't "scootch the material from the event horizon" because in the coordinates of anything approaching the hole, the matter does in fact fall in. However, you could study for example radiation from the matter. This is thought not to resolve the paradox for several reasons (note I gave a very similar answer to Can the event horizon save conservation laws ...

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With your description, if no radiation comes back from the surface of the black hole, the temperature should be the vacuum classical temperature, 0 Kelvin. BUT Hawking predicted a radiation coming out from quantum mechanical interactions with the vacuum at the limits of the event horizon. Hawking showed that quantum effects allow black holes to emit ...

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On the scale of galactic spiral arms, the central black hole is gravitationally utterly insignificant. I'll illustrate with an example, NGC 524. Of spiral galaxies (this is technically an S0, but there's still spiral structure) with measured black hole masses, NGC 524 has one of the most massive. Here's a picture of the galaxy: The visible disk has a ...

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So I take particle A and place it in space, then I place particle B 1,000,000 light years away from particle A. Alright. But, just to be sure: In astronomy, and (prehaps somewhat more recently) in cosmology and in physics in general, we understand this measure of "having been apart" as chronometric mutual separation. In your example this means ...

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