Black Holes

The simplest definition of a black hole is an object that is so dense that not even light can escape its surface. But how does that happen? The concept of a black hole can be understood by thinking about how fast something needs to move to escape the gravity of another object this is called the escape velocity. Formally, escape velocity is the speed an object must attain to "break free" of the gravitational attraction of another body. There are two things that affect the escape velocity the mass of the object and the distance to the center of that object. For example, a rocket must accelerate to 11.2 km/s in order to escape Earth's gravity. If, instead, that rocket was on a planet with the same mass as Earth but half the diameter, the escape velocity would be 15.8 km/s. Even though the mass is the same, the escape velocity is greater, because the object is smaller and denser.