So, they're saying that the outer surface could be made of charged particles.

These charged particles are like little magnets (not really but for the purpose of this explanation it works).

The strong magnetic field (from inside the star) fixes these tiny "magnets" in place. Kind of like how iron filings are pushed into specific shapes when exposed to a magnet.

The effect is so strong that the ions act in ways similar to a solid (ie not much movement of particles).

Just to add, freeze doesn’t always mean cold.

Radiation folds back on itself as it’s pulled back in by the magnetic force, causing interference that cancels out some/most of the radiation. This essentially freezes the electromagnetic wave radiation by literally stilling it/zeroing it out.

Not a physicist and I’m totally pulling that out of my spurious knowledge of EM wave interference.

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That’s an interesting question. Although I don’t think this explains the star, it might be of interest:

https://en.m.wikipedia.org/wiki/Magnetic_refrigeration