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.
White dwarfs are cool. I think it’s something like at least 1 quadrillion years to cool down to become a black dwarf.
I’ll add Neutron stars on top of that, the dead core of a star living on to slowly cool for an unfathomable amount of time. Also, Red Dwarfs eventually becoming Blue Dwarfs as they age is cool af too.
Once it cools down, what sort of matter will remain? Would it have a solid surface one could walk around on?
Not without shredding you due to high gravity and magnetism still.