What is black hole?

  A black hole is a region in space with a gravitational field so intense that even light can not get out. Because light can't escape, black holes can't be seen. They're detected by the difference in behaviour of stars nearer to the black hole. Stellar black holes are formed by the collapse of the centre of a massive star. This collapse also causes a supernova, or an exploding star, that blasts part of the star into space.