A galaxy is so large (e.g. the milky way is ~ 1 billion billions km in diameter!), and bodies are so far from each other that it is far from intuitive that there should even be a magnetic field, and it's even neatly aligned along the arms!
Like the Feynman diagram is in any case that a photon is transmitted between two charged objects, whether that photon is “real” or “virtual”.
I know there are physicists who interpret this as there being two distinct things, either particle-like excitations (photons) and more general excitations (not photons). These usually don’t think of Feynman diagrams as representing anything real.
But I also know there are some physicists who consider virtual photons “real”. And in that picture of reality, all EM interaction is “light”.
There are effects like quantum entanglement that seemingly bypasses this, but there is no way to extract useful information out of it.
there is no way to extract useful information out of it
The act of moving a magnet and thus changing the magnetic field at one point also induces a change in the electric field and vice versa, that's why you'll always hear talking about "electromagnetic" waves (which light, radio waves, etc are an instance of).
To make things even more interesting there is also this phenomenon: the magnetic field is created by moving electric changes, relative to the observer. If an observer moves at the same velocity as the electric charge it will not observe a magnetic field. It turns out that when you apply special relativity to the effects of electrical charges (coulomb 's law) you get a theory of electro-magnetism (Maxwell's equations). Magnetism this "follows" from the behavior of electrical fields and special relativity. That doesn't make magnetism less "real" but it hints at the intimate connection that the two forces have and what we now talk about them as "electromagnetism"
Answer; at the speed of light.