Timeline for How can a black hole have a charge, or be charged?
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13 events
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| Jul 13, 2021 at 0:37 | comment | added | user15381 | The Reissner-Nordstrom metric assumes that all the mass and electric charge reside at the physical singularity of the black hole: No, this is wrong. It's easier to talk about the simpler Schwarzschild solution. The mass doesn't exist at the singularity. The mass is an aggregate property of the spacetime. Nothing exists at the singularity, because it's not part of the spacetime manifold. | |
| Jul 12, 2021 at 23:37 | comment | added | Seb | Can the electric field lines starting within the event horizon of a charged black hole reach space outside the event horizon? The way I understand black holes (badly, I presume) they shouldn’t, and so there should be no measurable charge outside of the black hole. What am I missing? | |
| Jul 12, 2021 at 18:39 | comment | added | Daddy Kropotkin | In my answer, I really just meant that a black hole will accrete positive and negative charges in principle, and this works to keep the net charge of the black hole very small. The effect you're referring to with the external observer is an example of a loss of simultaneity, and we can't see exactly at the event horizon of an accreting black hole anyway in principle. However, measurements by the event horizon telescope of the shadow of a supermassive black hole agrees well with the predictions of the Kerr spacetime geometry, though future measurements might shed more light! ;) | |
| Jul 12, 2021 at 18:08 | comment | added | ProfRob | Just that you simultaneously talk about the Kerr-Newman metric and black holes accreting from their surroundings to become charged. There's something missing in the explanation. To an external observer, and in a static metric, nothing can be accreted through the event horizon, so the BH couldn't become charged. Is there some equivalent to Birkhoff's theorem that can be appealed to? | |
| Jul 12, 2021 at 16:46 | comment | added | Daddy Kropotkin | Hmmm... I'm not sure. As far as I understand, once you add fluid dynamics for the accretion disk, the( disk+Kerr background) spacetime is no longer static, and as far as I understand, fully general relativistic numerical simulations can handle this (nowadays), of course not perfectly. Perhaps I'm not understanding your point? | |
| Jul 12, 2021 at 15:14 | comment | added | ProfRob | All the metrics above are static. Doesn't that mean that none of them deal (accurately) with the accretion of mass or charge. | |
| Jul 12, 2021 at 14:31 | history | edited | Daddy Kropotkin | CC BY-SA 4.0 |
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| Jul 12, 2021 at 14:03 | history | edited | Daddy Kropotkin | CC BY-SA 4.0 |
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| Jul 12, 2021 at 13:55 | history | edited | Daddy Kropotkin | CC BY-SA 4.0 |
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| Jul 12, 2021 at 13:50 | history | edited | Daddy Kropotkin | CC BY-SA 4.0 |
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| Jul 12, 2021 at 13:13 | history | edited | Daddy Kropotkin | CC BY-SA 4.0 |
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| Jul 12, 2021 at 12:30 | history | edited | Daddy Kropotkin | CC BY-SA 4.0 |
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| Jul 12, 2021 at 12:24 | history | answered | Daddy Kropotkin | CC BY-SA 4.0 |