>Can't imagine what kind of crazy magnetic field action is going on in ultra-hot gas giants who are so close to their host star that their orbital period is 1-2 days.

Vaguely connected to this statement. Can anyone recommend any stories (preferably hard sci-fi, although I'm assuming anything tackling this sort of thing would automatically filter into that genre) regarding exotic elements, extreme conditions in space, or those sorts of things?

Like Neutron Star or Cannonball Express by Larry Niven. That sort of thing.

I just read through the recent Hannu Rajanaemi series (Quantum Thief, Fractal Prince, Causal Angel) which is all about that kind of thing. The Iain M. Banks novel "The Algebraist" is set mostly in the atmosphere of a gas giant planet and is pretty hard-sci-fi in outlook and plot.

Since you mention neutron stars, these are must-reads:

https://en.wikipedia.org/wiki/Dragon%27s_Egg

https://en.wikipedia.org/wiki/Starquake_(novel)

Someday I should read Baxter's Xeelee sequence, mentioned under "See also":

https://en.wikipedia.org/wiki/Xeelee_Sequence