Gravity's Lens - V2Image cropped - click to view
A black hole is an object so compact - usually a collapsed star - that nothing can escape its gravitational pull. Not even light. On Earth an object needs to be launched with a speed of 11 km/s if it is to escape the planet's gravity and go into orbit. But the escape velocity of a black hole exceeds the speed of light. Since nothing can travel faster than this ultimate speed, black holes suck in everything including light, which make them utterly dark and invisible. In this image, we can see a black hole, but only because of the background stars. Their light is bent and lensed by the hole, and the light of the stars which are most directly behind it surrounds the hole in a glowing ring.