Eh? Gravitation HAS been explained.
Gravitation is not a force as such, it is the "shape" of space-time...
Mass bends space, not gravity, gravity is the 'shape' of the bend that mass has created.
You know, ye-old rubber-sheet example and all that...

And black-holes have(apparently) been observed, kindof.
As matter falling in is torn asunder, just BEFORE the event horizon,
it generates huge amounts of x-ray radiation.
Some of this radiation manages to stay in orbit outside the event-horizon
long enough to get thrown off the north and south 'poles' of a spinning black-hole.
These x-ray "fountains" have been obverved many times...
Not really 'proof', but its the best we can get without visiting one, or making our own...