Black holes are cosmic objects that harbour a gravitational field so powerful that nothing, not even light or radiation can escape. They are forged in the furnaces of dying stars, that are of a sufficient size and volume.
An illustration of a black hole.
An artist's portrayal of a black hole in the Milky Way gallaxy.
Animated simulation of gravitational lensing caused by a going past a background galaxy; because light cannot escape black holes, this effect is perceived by an exterior viewer.
The merging of two black holes.
The black hole is the "cross" shape at the center of the galaxy.
A concept drawing by NASA showing the accretion lines from a black hole.