If a black hole is of infinite density but Zero diameter does that make it a 2 dimensional or a 1 dimensional Object

You mean the singularity, right. For the Schwarzschild black hole the singularity is just a point, that is zero dimensional. If the black hole is rotating, then the singularity gets stretched out into a ring. However, technically the volume of such regions is zero!

How common could a point black hole be? I thought for every black hole detected, the horizon has a size, like planet-sized for a stellar black hole, and much bigger for a galactic black hole.

For a solar mass black hole, the radius is about 3km. The radius is directly proportional to mass, so you can get an idea from that.

The event horizon and ( possible ) singularity are different Enthalpy. The much larger horizon 'cloaks' the singularity from the rest of the universe.

As far as I know naked singularities are a no-no, and primordial microscopic horizon ( small mass ) black holes should have evaporated long ago due to Hawking radiation.

 

But who knows, we may be able to create microscopic black holes using a large enough accelerator. The LHC is obviously too small.

Edited March 22, 201411 yr by MigL

How common could a point black hole be? I thought for every black hole detected, the horizon has a size, like planet-sized for a stellar black hole, and much bigger for a galactic black hole.

The opening statement about the zero diameter made me think the question is about the point-like singularity at the centre of a non-rotating black hole, as classically described by general relativity.