Was watching Rick and Morty on the Season 3 premiere and they have that very small planet that the family goes to to escape. The planet is humorously small in that it is noticeable round while walking. The planet also apparently has animals and breathable air for humans. At one point, Rick goes to the South Pole of the planet and goes into a cave that takes him to the core of the planet which is shown as being smaller than him, from what I remember and what it looked like.
Could a planet like this actually exist with all of these features, only being a few acres in size, at most? Would a breathable atmosphere be possible? Would a core be present at all?
To put it in more realistic terms, the planet would be the size of Manhattan Island in New York City but folded to be round.
Someone needs to do the math, using the densest material, how much it would take to have enough gravity to keep things on the surface from flying off easily.
My guess is, it can't be cartoonishly small like the Rick & Morty planet, but it probably can be significantly smaller than the moon.
Black hole. It can be absolutely miniscule.
I'm no astronomer but I'm pretty sure you can't walk on a black hole. And if you just place a black hole in the center of a hollow planet, it would necessarily create a cavity in the center so I don't think it would be stable.
Whatever the answer is, it must be stable and walkable.
Depends on the size of the black hole actually, you can make reasonably heavy black holes that are so small that it might actually not be possible for particles to fall into them.
You have to make them with some extremely well tuned lasers, and they'll produce enormous amounts of radiation that will likely steralise the planet anyway, but possibly feasible...