> - Why is there an assumption that just after a mass becomes a black hole the matter inside it suddenly compresses further when the actual gravity of the object has only slightly increased?
Yeah, that seems like an important thing to address. Black holes don't even have to be high density, or have much matter in the center at the time of formation. If you arrange enough big chunks of metal into a spherical-shell constellation, then drop them all toward their mutual center, they can reach the threshold to become a black hole before they even start colliding. What happens around that time, and what specifically does "singularity" mean (because I see people using it in very different ways).
> - Is there a maximum density of matter in the universe and if the black hole even reaches that?
> - Wouldn't you need that number to be infinite if the black hole itself is infinitely small?
Black holes are the benchmark for maximum density. The event horizon is always exactly at the limit. By "black hole itself" do you mean something other than the event horizon?
But that maximum density depends on size, smaller things can be denser and bigger things have to be less dense.
I can imagine it's something stupidly energetic. If you don't want them turning into a hot ball of neutrons first you're either going to have to spend a lot of energy keeping them apart or they are going to be orbiting a virtual center and it will take far longer for them to reach the center singularity than you expect. This will follow the laws of the 3(+) body problem so you won't be able to calculate a perfect impact, so the birth of the singularity will be shrouded in very high energy particles escaping.
> If you arrange enough big chunks of metal into a spherical-shell constellation, then drop them all toward their mutual center, they can reach the threshold to become a black hole before they even start colliding.
When I say "black hole itself" I imagine any combination of mass at it's center that provides enough density to form a gravitational pull that will trap light.
Yeah, that seems like an important thing to address. Black holes don't even have to be high density, or have much matter in the center at the time of formation. If you arrange enough big chunks of metal into a spherical-shell constellation, then drop them all toward their mutual center, they can reach the threshold to become a black hole before they even start colliding. What happens around that time, and what specifically does "singularity" mean (because I see people using it in very different ways).
> - Is there a maximum density of matter in the universe and if the black hole even reaches that?
> - Wouldn't you need that number to be infinite if the black hole itself is infinitely small?
Black holes are the benchmark for maximum density. The event horizon is always exactly at the limit. By "black hole itself" do you mean something other than the event horizon?
But that maximum density depends on size, smaller things can be denser and bigger things have to be less dense.