I have read this question:

If a Kerr-Newman black hole is like a charged, spinning, heavy magnet, what kind of magnet is it like?

If you are carrying a magnet, can you tell when you cross the event horizon of a black hole?

I know one of the questions is from astronomy but I am asking more about the physics, and especially QM and GR.


I understand that since black holes have mass, spin, and electric charge. Since we have rotation and electricity, we will have a magnetic field.

However, you should not imagine the electric (or magnetic, same thing) field as "escaping" the BH. It does not escape. What happens is, when the charges were swallowed by the BH, the lines of electric field remain "glued" to the BH, which then acquires a charge. Those lines of electric field have existed forever, they don't "escape" anything, and continue to exist after the charge is trapped by the BH.

So the magnetic field does not escape the black hole. What happens is, that the magnetic field lines are trapped by the black hole, so there are magnetic field lines inside the black hole and outside too.

What this does not answer is, whether if there is a magnet inside the event horizon, and another outside the event horizon, if those to magnets will repel or attract or not.

Since the magnetic field lines are there inside the event horizon, and outside too, for both magnets, they should repel or attract.


  1. If I have a magnet inside the event horizon, and one outside, will they repel or attract each other?

  2. Is that correct that the magnetic field lines are trapped and keep existing inside and outside the black hole?


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