Personally, I find Brown Dwarfs to be absolutely fascinating. An object that isn’t quite a planet and isn’t quite a star, but something in between.
What would one even look like? Would it look like a gas giant that’s glowing red, along with swirls of gas in its atmosphere like Jupiter? Or would it resemble a star and have a fiery surface like the sun? I prefer to imagine them as glowing gas giants but I don’t know how realistic that is.
Gas giants in general are fascinating to me as well, I really hope we send a probe into one of the gas giants with a camera before I die. I’d absolutely love to see what it looks like inside a gas giants atmosphere before the probe gets crushed by the increasing pressure as it descends.
I would be very careful with the kind of speculation the other commenter proposed. Those things are very popular science-ey and almost unverifiable at the moment, it’s hard to tell if there is even any actual academic research behind many of these “theories” that get thrown around by some laypersons. And even if there are actual publications behind such proposals, as in this case, the validity of their theses is far from certain. It is a very theoretical domain in which new knowledge can easily be “hallucinated” without much connection to physical reality, even - or in particular - by professions.