How can a magnetic field escape a black hole if light cannot?
May the force be with you...
A black hole can have mass, spin and charge, that’s it. All are measureable from the “point of no return”.
A moving charge creates a current which creates a magnetic field. I suppose that is the magnetic field they measured but I don’t have access to the paper.
Gravity escapes. But I’ve been wondering about that, too. Magnetic field lines: Can they escape? If not, then what’s the big problem here; if magnetic field lines can’t escape, then we shouldn’t be surprised that the magnetic field of a black hole is wimpy, right? But then, I’m not a physicist, as should be obvious to any such person reading about my total state of confusion!