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I have read this question:

Charged particle is accompanied with EM radiation (has field that falls with distance as 1/r) when it moves with acceleration.

Does a constantly accelerating charged particle emit EM radiation or not?

It emits light, because it "stirs up" the electromagnetic field. To understand this, just dip your finger into a still pond and move it in a circle. Water waves will emanate from your finger. These waves have energy, which means energy is being taken away from you. Same goes for the charges. In fact, this follows almost automatically from the finite propagation speed of light. The electric field of a stationary charge obeys Coulomb's law. If the charge suddenly starts moving, the field won't obey Coulomb's law anymore, but it can't instantly change everywhere because of the finite propagation speed. Instead a "shockwave" of information goes out from the charge at speed c. This shockwave contains electromagnetic energy and travels at the speed of light -- it is light.

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Why does an accelerated charge radiate away energy?

So based on these, two things come to mind:

  1. all accelerating charges emit EM radiation (because they stir up the field)

  2. nothing can escape a black hole (neither should the EM radiation)

And I cannot reconcile these two at the same time, because if light (EM radiation) cannot escape the black hole, then how does it emit it if it is accelerating?

Question:

  1. Does an accelerating charged black hole emit EM radiation?
Árpád Szendrei
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  • Can two charged black holes interact? Will their courses change? If you vibrate a hole will it emit radiation? Seems so. Like when you vibrate an electron. – MatterGauge Feb 14 '22 at 23:33
  • Could two charged black holes circle one another because of charge? – MatterGauge Feb 15 '22 at 00:18
  • Off course they emit energy. How are they accelerated? In an electric field. – MatterGauge Feb 15 '22 at 00:22
  • Many of your black hole questions have the same answer - there is nothing inside a real black hole. Everything that ever falls in remains at the horizon forever, including the original matter of the collapsed star. – safesphere Feb 15 '22 at 15:51
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    Also note that it is not trivial to accelerate a black hole. You cannot simply push or pull it like in your picture. You need either strong tidal gravitational forces or a strong electromagnetic interaction. – safesphere Feb 15 '22 at 16:30
  • @safesphere what about maybe a (high speed) collision with another celestial object? – Árpád Szendrei Feb 15 '22 at 16:31
  • An object cannot literally “collide” with a black hole like with another object, because a black hole doesn’t have a surface. The black hole instead would consume the object or a part of the object. In this process indeed there will be some momentary tidal forces affecting the symmetry of the black hole, so some momentary bursts of radiation (gravitational or electromagnetic) may be possible. – safesphere Feb 15 '22 at 16:38
  • Relevant I think: "How does gravity escape a black hole? - PBS Space Time" https://youtu.be/cDQZXvplXKA also touches on how EM field "escapes" the black hole – Rodney Feb 15 '22 at 23:02

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Yes, it will radiate. The light does not come from inside the black hole. The accelerated charge of the black hole affects the electromagnetic field around but outside the event horizon.

You could ask the same question you are asking now about gravitational waves. Binary black hole systems radiate gravitational waves, even though a gravitational wave that fell into a black hole could not escape.

Andrew
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  • But don't the EM waves propagate from the space immediately surrounding the charge, ie in the blackholes event horizon. And thus cannot escape? Isn't the reason that gravitational waves can propagate outwards is because it is the fabric of spacetime itself waving, instead of something IN that fabric? Can you give me a link to a source? – jensen paull Feb 15 '22 at 00:16
  • Also if your correct. Then wouldn't blackholes lose energy, WITHOUT hawking radiation.... – jensen paull Feb 15 '22 at 00:17
  • An immediate Google search seems to suggest they do not emit any EM radiation – jensen paull Feb 15 '22 at 00:18
  • @jensenpaull They would loose or gain kinetic energy. Not mass. – MatterGauge Feb 15 '22 at 00:20
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    @jensenpaull I am not sure if anyone has actually done this calculation or not. But it's pretty clear that you will have radiation. A charged black hole will act as a source term for the electromagnetic stress-energy tensor in the Einstein-Maxwell equations. There's no problem with conservation of energy, because an accelerating black hole needs an input of energy from somewhere; that is also the source of the radiated energy. (A stationary charged black hole wouldn't radiate). – Andrew Feb 15 '22 at 00:22
  • I'd be interested if you could link to a result from your google search. All I find is that real black holes are electrically neutral, so don't emit EM radiation. But that isn't relevant for the question. – Andrew Feb 15 '22 at 00:22
  • I haven't studied general relativity. But wouldn't the decrease in the blackholes KE also decrease the blackholes apparent mass though. Although I know that KE is frame dependant so I could be wrong – jensen paull Feb 15 '22 at 00:22
  • You're correct I didn't specify in my Google search that the black hole was charged. However. Thought experiment. If someone went into the blackhole with a transmitter, they could tell us what the inside of a blackhole would look like as they could send a signal out of the blackhole. I haven't studied much of this, but this seems to go against everything that I HAVE been told – jensen paull Feb 15 '22 at 00:28
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    @jensen From https://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/black_gravity.html In this sense the black hole is a kind of "frozen star": the gravitational field is a fossil field.  The same is true of the electromagnetic field that a black hole may possess. – PM 2Ring Feb 15 '22 at 00:28
  • If light cam escape from the event horizon then why is it called a black hole? You say that the light doesn't come from the below the event horizon, but the charge effects the field outside of the event horizon. But for the em waves to propagate there must be an initial db/dt de/dt coming from below the event horizon to "start" the EM Wave off outside the horizon? – jensen paull Feb 15 '22 at 00:39
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    @jensenpaull Light isn't escaping the black hole. There's some EM field surrounding the black hole when it is stationary. Then you accelerate the black hole. The EM field near the horizon will follow the horizon. The EM field a little further away from the horizon will obey Maxwell's equations. Maxwell's equations tell the field at a given point in space how to change, given what the field looks like in a neighborhood around that point. It doesn't matter if the field lines are connected to a point charge or a black hole. The field lines are changing. This will lead to a wave solution. – Andrew Feb 15 '22 at 00:45
  • @jensen Nothing can come from below the EH (event horizon), that includes electromagnetic influences and gravity. Charged bodies falling towards the BH affect the electromagnetic field & spacetime curvature outside the EH. Once they've crossed the EH, those changes are locked in, or "fossilized" in the terminology of that Usenet article I linked earlier. – PM 2Ring Feb 15 '22 at 00:52
  • OTOH, a distant observer never sees anything cross the EH anyway, and what nearby observers see depends on whether they're falling into the BH or not. – PM 2Ring Feb 15 '22 at 00:54
  • Black holes bend light by bending space. This way of thinking of black holes works when you're rolling balls on a trampoline. But the trampoline fails in this case because it doesn't explain red shift. Stand between a black hole and me and shine a light and I'll see it Red Shifted because the black hole is pulling space away from us slowing down the frequency of the light. Which means time is passing more quickly for you. It also means when you cross the event horizon you're still emitting light. It just gets red shifted until it's frequency is 0. The universe will end before I get to see it. – candied_orange Feb 15 '22 at 19:26
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You need to take into consideration how the hole is accelerated. That's because other charges create a field. And just as two electrons, interacting by virtual photons, can create a real photon not coming out of themselves, a hole can do this to. And as @Andrew says, two holes can emit real gravitational waves (real gravitons), not coming out of the hole. The internal of the hole doesn’t change. Only the surrounding condensate of photons (or gravitons).

Brehmstralung

MatterGauge
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An inertial observer should see the black hole (electrically charged) emit radiation in accordance with Maxwell's equations.

Michael Ejercito
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