Answer:
Schwarzschild radius
Explanation:
A black hole is defined as that object from which light cannot escape form the surface of the object because object is very small an very dense. There are numerous black hole sin the universe.
Black hole is well understood by the concept of "escape velocity". Escape velocity is the speed of any object to break the gravitational pull from another object.
Escape velocity depends on mass of the object and the distance from the center of the object ( how big or small the object is ). If the object is smaller or more denser, than the escape velocity is more. If we squeeze our earth to a radius of about 9 mm sphere, then the escape velocity of any object becomes equal to the velocity of light.
And the radius of any object which have an escape velocity which is same as the velocity of light is known as the 'Schwarzschild radius'.
Any object which is smaller than the "Schwarzschild radius' has an escape velocity more than the speed of light and is termed as a black hole.
Thus, any object which is squeezed beyond the Schwarzschild radius be becomes a black hole.
