[The Scientist (OP)]

Black holes are very strong, but what makes them that strong? Please elaborate with explanation. Thanks all!

[ukmicky]

Matter, lots of matter , so much matter all squashed into such a small space that the  gravity it produces bends and contorts space so much that their is no path availiable leading out for any photons to escape and be seen .

 

[JP]

To elaborate a bit on ukmicky's point, our best models of the non-gravitational forces say that they're carried by particles zipping around in space-time, and that these particles can't move faster than the speed of light.

Gravity appears to be caused by a bending of space-time. 

If you bend space-time enough, the force-carrying particles are blocked from taking certain paths, which is why gravity can beat out all other forces in a black hole. 

Put another way, if you dangle a rope through the event horizon of a black hole, space-time is bent enough that the force-carrying particles on one side of the black hole can't reach the particles on the other side of the black hole, so the rope can't hold itself together because of gravity, and will be torn apart if you try to pull it out.

There are theories out there now that try to treat gravity as a particle process as well.  In that case, I'm not sure how they explain that it can beat out all other forces.

[Soul Surfer]

Powerful and strong are not properly defined scientific terms.  It is true that black holes with a few solar masses have very intense gravitational fields when you are close to them but these fields are no different from a star of the same mass when you are at the distance of a planet that might have been orbiting the star.  the mass energy of the black hole  (m.c squared) is also no different from a star of a similar mass.  the main property of a black hole is that it is extremely small  just about one mile across for every solar mass they contain.  This makes them extremely difficult to fall into.  Almost all single objects falling towards the hole will perform a tight orbit and the exit quickly like a comet. An isolated black hole is almost undetectable.  black holes only become powerful radiators of energy when large quantities of material fall towards them and start to orbit the hole (like a quasar  qv )  because of the friction between the material.  The orbital material then has to loose about half of its mass energy by radiating it away as light or particles in order to get into the hole.  A "feeding"  black hole is the most efficient way of turning mass into energy

[CPT ArkAngel]

What makes a black hole so strong is its size in comparison to its mass. It is of the ultimate density in the Universe, and you can go near it where there is an ultimate acceleration (or gravity). Both, the density and the acceleration are not infinite, in my opinion (we are in a quantum world). 

[jartza]

Pull of gravity is moderate at the event horizon of a very big black hole.

Pull of gravity felt by a person in a space vehicle staying still at the event horizon of a suitably large black hole is same as the gravity on Earth. So climbing up a ladder in the vehicle is not a problem.