Q&A: Black Holes
"The gravity of a black holes falls off inversely as the square
of the distance?" Sorry what does that mean exactly?
It means that as you get three times as far away, the gravity is
nine times weaker, etc. This is a general rule discovered by
Newton that applies to all objects that have mass. By balancing
gravity with the acceleration due to orbital speed, it is
possible to estimate the mass of the object producing the
gravity. This is the way that astronomers weigh the Earth, the
moon, stars, black holes, galaxies, etc.