Black holes are so massive they deform space and time, so dense their centers are called "points at infinity," and are absolutely black because even light can't escape them.
So what would happen if you were sucked into one?
If you were to step into a black hole, your body would most closely resemble "toothpaste being extruded out of the tube," says Charles Liu, an astrophysicist who works at the American Museum of Natural History's Hayden Planetarium.
According to LiveScience.com:
"First of all, you approach the speed of light as you fall into the black hole. So the faster you move through space, the slower you move through time," Liu said. "Furthermore, as you fall, there are things that have been falling in front of you that have experienced an even greater 'time dilation' than you have. So if you're able to look forward toward the black hole, you see every object that has fallen into it in the past. And then if you look backwards, you'll be able to see everything that will ever fall into the black hole behind you.
"So the upshot is, you'll get to see the entire history of that spot in the universe simultaneously," he said, "from the Big Bang all the way into the distant future."
Liu also explains the effects of other universal forces such as relativity on the hapless person who would encounter a black hole.