– how come black holes have different density if they all have a singularity that is infinitely dense?

Question

– how come black holes have different density if they all have a singularity that is infinitely dense?

In: 3

Answer 1

That is referring to the density of the event horizon. The singularity is infinitely dense due to zero volume but the event horizon has both a volume and mass so it has a real density. All the mass is still contained within the singularity at the centre of the black hole. The larger a black hole is the less dense it is as the event horizon grows with the cube while the mass grows linearly. Again the singularity just grows in mass as it has no volume.

Singularities are a result of incomplete theories to describe black holes. They are an approximation. Until we have a theory of quantum gravity they are all we have.