How Do We Detect the Charge of a Black Hole?

superg33k
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So how do charged black holes work?

If its photons that are the carriers of the electromagentic force, and photons can't escape from a black hole. How can anything external to a black hole tell if it's charged or not?
 
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The observable characteristics of black holes are external phenomena...for example the charge and spin, if any, would be that which happened to exist at the moment the horizon was formed during initial collapse... and any changes as might accrete over time.

Once the black hole is formed there is no observable causal effect thru the horizon...its all "black" inisde...we can only observe what was formed outside the event horizon.
 

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