Ask A Scientist© Astronomy Archive

Question:  If the gravitational force of a black hole is so strong that not even 
light can escape, how can the force of gravity/gravitons escape to affect matter 
outside the black hole and create the accretion disk that allows us to detect
the black hole?
jack w ryan

Answer:  In relativity, we no longer think of gravity as a "force".  Spacetime
in the vicinity of a very compact mass becomes badly distorted.  A shell forms
around the mass from which nothing can escape.  The inside of this shell is what 
we call the "black hole".  Spacetime outside of the shell is also distorted.  A  mass that is
outside of the shell will be subjected to an acceleration toward the center of
the shell by the distortion of spacetime.  But nothing has "escaped" from the
black hole to cause this acceleration.
In other words, the concepts that govern our everyday language no longer apply.
jlu