In order to escape the gravitational pull of the earth, a rocket must go 25,000 miles per hour. If it goes less than this, it will fall back down. This speed is known as the escape velocity of earth. If a planet has stronger gravity, the escape velocity will be even greater.
Basic Black Hole Theory
The theory behind a black hole is the idea that if enough mass is in one location, the gravity would be so great that the escape velocity would be 186,000 miles per second so that even light could not escape. This, of course, is assuming that light can be affected by gravity. No one has ever seen a black hole since no light could escape one if it existed.
Black Holes Are Not Proven
The problem black holes are supposed to fix is this: if the big bang theory were true, the matter should be evenly distributed in space. Since matter is not evenly distributed in space (we have clumps of matter called galaxies, then zillions of miles of nothing between) the believers in the big bang theory are trying to explain why. They are trying to say, “There is matter in between the clumps but we can’t see it because it is in black holes.” Actually, they are arguing from a lack of evidence not from evidence. The existence of a black holes is not proven.