"Strong gravity" refers to a situation where the force of gravity is very powerful or intense. It means that objects or matter are pulled towards each other with a great amount of force. Full definition
To properly describe these extreme objects, physicists need a more profound theory that can deal with strong gravity on tiny scales — a quantum theory of gravity. (newscientist.com)
Black holes are areas with such strong gravity that not even light can escape. (sciencedaily.com)
A black hole can not be seen because strong gravity pulls all of the light into the middle of the black hole. (educationworld.com)