system
Given the following post, respond as if you're commenting on Reddit:
human
How can both black holes and gravitons exist?

If gravity is carried by particles that move at the speed of light, how is it possible for a black hole to transmit gravitational effects to outside its own event horizon?
gpt
Actually it's not necessary to think about gravitons (quanta of the gravitational field) in order to have this question-- the same applies to the classical gravitational field and gravitational waves, the latter of which are how changes in the former propagate, and do so at the speed of light. As a star collapses, matter at the center is getting denser and denser, which is making the gravitational field inside the star stronger. These changes in the field propagate outward from the center of the star to the stellar interior at the speed of light, and continue to do so during the collapse, continually modifying the field. Eventually, the star may collapse inside its own Schwartzschild radius. After that point, the gravitational field outside that radius is mostly unchanging and is a solution to the vacuum Einstein equations (essentially vacuum because the matter density is small away from the singularity.) The black hole doesn't have to transmit any more effects: the state of the field (classically, the geometry of the spacetime) is to a first approximation quiescent, and test particles move in that field along the geodesics. 

In other words, the motion of test particles is affected locally by the state of the gravitational field, which was generated dynamically by stellar collapse and experienced changes that propagated through it at the speed of light during that volatile time. The test particles aren't actively interacting with the singularity and aren't sensitive to any dynamical processes still ongoing inside the horizon, due to the presence of the horizon.