11ac1064_ions___Astronomy___Black_Holes__Question
[Date Answered] August 21, 2007 [Questioner (age, location)] Mark (New Zealand Christchurch) [Answer] The gravitational force is a function of the product of the interacing masses and the inverse of he square of the distance between them. Black holes masses are enormous, for example, the giant elliptical galaxy M87 is believed to contain a supermassive black hole of several billion solar masses at its center. The observations indicate that approximately 3 billion solar masses are concentrated in a region at the galactic core that is only about the size of the Solar System. [Question] 
What causes black holes to have such a gravitational pull?
Quickie Questions - Astronomy - Black Holes