A black hole is a region of spacetime enclosed by an event horizon.
A black hole is formed by the collapse of massive objects. If the heat and pressure supplied by the fusion of the material within the star is less than the gravitational pull inward, the object may collapse to form a white dwarf, a neutron star, or (if it is massive enough) a black hole. .
A black hole is termed "black" because nothing can escape from within it, not even light. Everything that passes through the event horizon is gone from the observable universe. .
A black hole is a region where matter collapses to infinite density, and where, as a result, the curvature of spacetime is extreme. .
Event horizon .
The event horizon defines the boundary of a black hole behind which nothing, not even light, can escape. .
Consider an event (a given position at a given time) in spacetime. Now imagine that light rays shoot out in all directions from this event. If none of them can escape to an infinite distance then that event is inside the event horizon. If any can escape, that event is outside the event horizon. .
You can think of the horizon as the place where the escape velocity equals the velocity of light. .
The horizon has a very large velocity, moving outward at the speed of light. .
Near the event horizon, space itself is believed to be twisted and swirled around in ways ordinary intuition cannot grasp.
Singularity .
The center of a black hole; .
where matter is crushed to infinite density; .
the pull of gravity is infinitely strong; .
and spacetime has infinite curvature. .
Thus, it's no longer meaningful to speak of space and time, much less spacetime. Jumbled up at the singularity, space and time cease to exist as we know them. .
An object whose density is infinite.
Gravitational Waves [site] .
Predicted in Einstein's General Theory of Relativity. .
Gravitational waves are disturbances in the curvature of spacetime caused by the motions of matter. .
Moving at the speed of light, gravitational waves do not travel "through" spacetime; the fabric of spacetime itself is oscillating.
