Blackholes

What is a black hole and why are they "black"? What is the Schwarzschild radius? What is the event horizon? Black holes are the cold remnants of former stars, which have very powerful gravitational pull. No matter can escape this gravitational pull. Every thing including light gets pulled by the strong gravity causing this area black. The Schwarzschild radius is when the speed of escaping object equals the speed of the light and the object could no longer be seen. The Earth’s Schwarzschild radius is about a centimeter; the Sun’s is about 3 km. The event horizon is an imaginary spherical surface surrounding a collapsing star, with a radius equal to the Schwarzschild radius, within which no event can be seen, heard or known about by an outside observer (Pg. 594).