Black holes have a stronger gravitational force compared to other celestial objects because they have an extremely high concentration of mass within a small volume. The gravitational force of an object depends on two factors: the mass of the object and the distance from the object.
In the case of a black hole, the mass is concentrated in an extremely small region, called the singularity. The singularity is a point of infinite density where the laws of physics, as currently understood, break down. Surrounding the singularity is the event horizon, which is the boundary beyond which nothing can escape the gravitational pull of the black hole.
Because the mass of a black hole is concentrated in such a small volume, the distance from the singularity to any given point near the black hole is relatively short compared to other objects with similar mass. The combination of the immense mass and the close proximity to the singularity leads to an extremely strong gravitational field.
According to Einstein's general theory of relativity, the curvature of spacetime around a massive object determines the strength of its gravitational field. In the case of a black hole, the curvature is so extreme that it creates a gravitational pull so strong that nothing, not even light, can escape it within the event horizon. This is what gives black holes their name—they appear "black" because their gravity is so strong that even light cannot escape from them.
It's important to note that our current understanding of black holes is based on the general theory of relativity, but there are still many unanswered questions about the nature of black holes and the behavior of matter within them.