# Gravity of black hole and that of star that formed it [duplicate]

Since the black hole is formed by a star of high mass after supernovae it should have less mass than original star. Then how the gravity of black hole is much stronger than a star that formed it? Since F∝Mass of object.

## marked as duplicate by Qmechanic♦Apr 25 '18 at 6:42

Because $F$ is in fact proportional to $M/r^2$ (thinking of gravity in a Newtonian way). The mass that remains has been compressed into a small radius. Once a certain mass is inside it's Schwarzschild radius then it is a black hole.