http://www.sciencealert.com/the-magnetic-field-just-outside-our-black-hole-has-been-studied-for-the-first-time reported strong magnetic fields escape out of black holes. Does that rule out photons being a component off a magnetic field since light/photon are trapped by the black hole?

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    $\begingroup$ No - the fields are outside the blackhole, just closer than have been observed previously $\endgroup$ Dec 29, 2015 at 4:46
  • $\begingroup$ @MartinBeckett When the material is consumed by the black hole it creates a magnetic field. Does that consumption happen inside the black hole or outside the singularity? $\endgroup$
    – Muze
    Dec 29, 2015 at 5:03

2 Answers 2


The magnetic fields in question are generated by the motion of charged gas in the accretion disk i.e. outside the black hole. So it is not the case that the black hole generates the magnetic field which then has to somehow escape through the event horizon.

The literature contains references to the field lines threading the event horizon, but I suspect this is just rather casual wording. Real black holes do not contain a true horizon as the true horizon takes an infinite coordinate time to develop. At best the system will have an apparent horizon. It isn't clear to me whether magnetic fields can thread an apparent horizon, but in any case the field lines will become very distorted in the immediate vicinity of the horizon and the end result will be essentially identical to the field lines threading the horizon.

It has long been known that active galaxy nuclei possess a strong magnetic field, but what is new is the realisation of just how strong these fields are.


I want to address this:

Does that rule out photons being a component off a magnetic field since light/photon are trapped by the black hole?

It is simpler to think of magnetic fields within classical electrodynamics.

The magnetic field can be described quantum mechanically as the result of virtual photon exchanges. See my answer here on how this happens, and in the answer to the duplicate question.

To introduce virtual photons in the strong mix of the gravitational field of the black hole will not aid in understanding what is happening and in the end it will give the same mathematical result following a much more complicated path.


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