Black holes
Here is a nice artist's impression of a black hole:
Source: http://www.roe.ac.uk
So, what is a black hole and how are they formed? Massive stars, say 1000 times the size of our sun, are so heavy that when they explode the matter contained within the star cannot escape its own gravity. Therefore when a massive star explodes the matter collapses in on itself and is crushed until it forms a tiny, microscopic hole with the same amount of matter as the original star. This large amount of matter, squeezed into such a tiny space, no bigger than the size of a pea, is what makes black holes so powerful!
A black hole, with its mind boggling gravity, is so powerful that is will destroy anything that come close enough to it – even super massive stars!
Hundreds of black holes have been discovered in our very own galaxy, the Milky Way. At the centre of the Milky Way lies a super massive black hole, a million times larger than normal. This enormous black hole is so powerful that it spins all of the stars in the Milky Way around it, at incredible speeds.
Once formed black holes will always exist, forever tearing apart stars. There are billions of massive stars in our universe that will one day become black holes. Could they eventually destroy our universe?
here is a wonderful video about black holes, by the BBC:
http://video.google.co.uk/videoplay?docid=7052861094451788348&q=black+hole+duration%3Along
Another video about the black hole at the centre of the milky way:
http://video.google.com/videoplay?docid=6199067060728714818&q=black+holes+duration%3Along