The most exciting idea to me that JWST has bolstered is primordial black holes. Many models already predict them but JWST has provided the first good indirect evidence in the form of too-early galaxies. The models that predict PBHs predict that.

If they exist, they would not be constrained to stellar mass and above. There could be a population of little black holes floating around. Anything under the mass of a decent size asteroid would have evaporated by now but anything that mass and above would still exist.

They are a dark matter candidate, and one that doesn’t require new physics. But even if they don’t account for a significant amount of dark matter they still probably exist.

The most exciting thing about PBHs is that one or more may exist in our solar system. They might have been captured over billions of years. Finding them would be incredibly challenging, especially if they are low mass, but if we did it means we could directly examine and experiment on a black hole.

It could be something with the mass of a large asteroid but the size of a hydrogen atom. We could only find it by its gravitational effects. It would be utterly invisible otherwise unless it encountered matter and even then there might only be a tiny gamma ray flash, a nano accretion disc that lasts femtoseconds. We might also find smaller objects that appear to be orbiting nothing and find it that way.

Directly accessing one could allow us to test theories of quantum gravity and things like string theory, and maybe more. A black hole could be like a Rosetta Stone of deep fundamental physics.

The film Interstellar involved using plot magic to visit a black hole and solve physics, but this would allow it for real. It would just be an itty bitty one.