Supermassive black holes have masses of one million to one billion Suns and are believed to have formed long ago from giant gas clouds or the collapse of clusters of many stars. A third class was discovered in April of 1999 and dubbed middleweights. Scientists say that anything sucked into a black hole disappears from the observable universe. Nothing, in fact, can escape from a black hole. A black hole is so powerful it even bends the light around it.
Black holes come in different sizes.
The entire mass of the Earth could be squeezed into a black hole the size of a marble. Scientists theorize about them by measuring their effects. Clues include powerful X-rays or gamma rays that are observed coming from invisible objects. In this Hubble Space Telescope image, astronomers saw something massive in the middle of this galaxy that was sucking and swallowing the disk of spinning gas. Measurements showed the gas swirling at a superfast 1.2 million miles per hour.