Gravity is not a force that acts on objects with mass. Instead, gravity is a curvature of spacetime. This means that the presence of mass curves the fabric of spacetime, and this curvature affects the motion of objects, whether they have mass or not.

A photon is a massless particle, but it still travels through spacetime. When a photon travels through a region of spacetime that is curved by a massive object, such as a black hole, the photon’s path is bent by the curvature of spacetime. This is why we see light bend around stars and other massive objects.

The event horizon of a black hole is the point at which the curvature of spacetime becomes infinite. This means that no matter how fast a photon is traveling, it cannot escape the event horizon. This is why we say that nothing, not even light, can escape the event horizon of a black hole.

Here is a simple analogy to help you understand how gravity can affect massless particles. Imagine a bowling ball placed on a trampoline. The bowling ball will cause the trampoline to sag, and this sagging will cause a marble rolling towards the bowling ball to curve towards it. The marble does not have mass, but it is still affected by the curvature of spacetime caused by the bowling ball.

The same thing happens with photons and black holes. The curvature of spacetime caused by a black hole is so strong that it can even bend the path of light. This is why we see light bend around stars and other massive objects, and why nothing, not even light, can escape the event horizon of a black hole.