But there is a huge problem with them. Like Alfven, I am against the idea of frozen magnetic fields. Frozen fields were invented to explain how magnetic fields can exist, without the need for electric currents. At that time they thought that space was a very good isolator. Thanks to laboratories and satellites we now know different.
With my background in electromagnetism, I have to go one step further: frozen fields are physically impossible. The papers and text-books about them show false usage of induction laws. As if magnetism behaves like a current, like in a waveguide with electromagnetic waves. Sadly this is completely false. Induction in gasses or plasma behave a bit like those in a fluid, and they disperse the magnetic field. A bit like eddy currents. That is also what we see in our laboratories.
But magnetic fields can easily be caused by electric currents instead, because any electric current creates a magnetic field. This field is stronger when we measure closer to the current. So we can get very strong magnetic fields as we see inside young galaxies. Link: https://www.discovermagazine.com/the-sciences/weirdly-strong... So we have electric plasma currents, instead of "magnetic ropes". Like in our laboratories. But I am not sure whether the community is ready to accept that..
Instead of the dynamo model, strong electric currents can easily come from nuclear explosions. These have been reported, but due to the secrecy they are not openly reported. Just a magnetic field can create a homopolar dynamo in an electric current. Currents are usually circular, but in a large space and very high speeds, the charge can take a long time to come around. It will be very interesting to actually measure the scale at which these occur.
Now if we have a black-hole like object in the centre of a galaxy, that spews out matter into 2 main directions. Because it also has a magnetic field, it is very likely that this matter has a certain charge. So this creates a current in the galaxy, which also generates the magnetic field. This how I think the magnetic field is generated.
The strength of these electric currents is in the order of 1/R, where R is the distance travelled. That is because currents are usually concentrated into one direction, like lightning, and only resistance hinders it. Magnetic objects encounter a force of 1/R^4 because magnetic objects have 2 poles. So these electric currents can transfer energy over very long distances.
As this matter-beam reaches the edge of the galaxy, it will turn around and go back to the galaxy. And because it has some charge, it will create a polarizing field in the halo.It would be interesting to see if there is also some sustained charge in these halos.
https://fermi.gsfc.nasa.gov/science/constellations/pages/bub... I suspect that the Fermi bubbles might have an opposite charge.