well, probably it's solid to gas ratio is similar to earth. and probably, the lit part represents around the same strata as the ionosphere, which on our planet, and all larger planets, light up with auroras.
once the mass gets to a certain point, it moves from just having a strong magnetosphere (they call the sun's magnetic shield the heliosphere) to having a massive amount of energy from the internal dynamo under the crust, that it is constantly ionizing the atmosphere. nearest we get to seeing it is in infrared and x-ray bands these "coronal holes" which are shifting zones of strong magnetic alignment, probably a combination of the plasma carrying the current and the eventual subdivision of the magnetic fields due to the enormous amounts of ferromagnetic molten rock deep inside.
i don't think stars are gas inside, how would they get to forming into things like magnetars, otherwise.
magnetars are absolutely mindblowing star types. their magnetic fields are so strong they destroy everything that comes close.
https://en.wikipedia.org/wiki/Magnetar