SCIENCE: NEUTRON STARS & BLACK HOLES

Matter from a neutron star--the core that sometimes survives a giant star's explosive end known as a supernova--is so dense that a teaspoon of it would weigh several million tons. If sufficient matter remains after a supernova the remaining debris can continue to collapse from its own gravity and be squeezed together within a single tiny point (singularity) known as a "black hole." Nothing--including light--can escape a black hole once it enters the "event horizon," the point where matter is pulled into the black hole. The "size" of a black hole refers to the size of its event horizon, not the hole itself. As the black hole traps more matter it gains more mass and therefore more gravity and a larger event horizon. Matter around the black hole forms a disk-shaped pattern called an "accretion disk." The rapid spiraling of matter entering the black hole from the accretion disk heats the matter to the point that it emits x-rays beyond the event horizon. Although astronomers cannot see a black hole they can see these x-rays outside of the event horizon with special telescopes. [Source: Will Black Holes Devour the Universe? & 100 Other Questions & Answers About Astronomy by Melanie Melton] More good information about black holes can be found at http://imagine.gsfc.nasa.gov/docs/science/know_l2/black_holes.html.