Mom, did you know there’s a density limit? Density is mass divided by size! If an object reaches the density limit it will become a black hole. If you have an object that is not homogeneous it can be more than the density limit in some places and less than the density limit in other places, and then in some places it’ll be a black hole and in others not. And so the object will swallow up itself!
(exactly what we are talking about when the picture was taken)