For a body of a given mass, the radius beneath which that body's gravitational field will take on
the properties of a Black Hole, preventing the escape of all matter and energy. The
Schwarzchild radius represents an immensely compacted state - for example, it has been calculated that the Schwarzchild radius of the
entire Earth is of the order of one centimetre. The forces required to collapse a
body to this extent are such that only the most massive stars (far more massive than the
Sun) have the potential to reach it.