THE IDEA THAT A BLACK HOLE could possibly exist came from an English rector, John Michell. In 1783 he calculated that the force of gravity exerted by a massive star could prevent light from escaping its surface. Michell's work was largely forgotten for 200 years. In 1971 astrophysicists noticed flickering x-rays coming from the constellation Cygnus, 6,000 light-years away: the radiation indicated that a black hole was apparently circling a star. As with any black hole, it formed as a star ran out of fuel and collapsed in on itself. If the sun were to somehow become a black hole, it would be less than three miles across, trapping light in the warped space that enfolds it. For Earth to become a black hole, it would be the size of a marble.
The first black holes in the universe arose nearly 14 billion years ago, contends Abraham Loeb, an astrophysicist at Harvard University. At that time, gas began to condense into clouds that fragmented into massive stars 100 times the size of the sun, which in turn collapsed into black holes. Fortunately, the spinning of early galaxies limited the growth of the black holes at their cores, allowing stars to form.