Speed of gravity

Does anyone know of a reference/literature on the speed of gravity? I recall hearing it is same as speed of light.
The main question I have is: If speed of gravity wave is same as speed of light, then is it physically possible to have a black hole. Just like a charged particle cannot be accelerated to speed of light, else it will start bleeding virtual photons as real photons via Cerenkov Mechanism (let's forget relativity based mathematics and try to only involve "english" explanation)... Shouldn't it be that in order for gravity to be strong enough to trap light (aka, formation of black hole), the speed of gravity wave has to be faster than that of light?