Why do black holes have high gravity?

All right, let's go all the way back, before a dreaded black hole was formed. Let's say we have a star. A huge star. A star way, way bigger than the sun (if you can believe it). read more

Very large or infinity. This is because of very low volume, close to zero. Black holes have very low volume which makes its density very high. This high density results in large bending of space-time fabric and hence contributes to strong gravity. That is why black holes have very strong gravity. read more

But the black hole solutions have a vanishing energy-momentum tensor and no matter anywhere at all: their Ricci curvature is therefore also vanishing, meaning that there may be tidal forces and a very large gravity corresponding to a non-vanishing Weyl curvature in the exterior and interior, and also no matter at all in the interior except perhaps right at a singularity in the curvature in which always appears in the interior in such solutions. read more

Black hole singularities have 0 volume, so any finite mass they might have will net infinite density, and infinite gravity (since you can get infinitely close to the central mass). Black holes themselves are regions surrounding the singularity, within which escape velocity is greater than c. read more