Stars and galaxies cause a curvature of space-time. When a star runs out of fuel, thermonuclear fusion ceases. Without the radiation pressure resulting from fusion, the star cannot support itself. It contracts due to gravity. If the star is very massive, it will collapse to a singularity or a point of infinite space-time curvature. The event horizon of a black hole is the surface that bounds the region from which nothing, not even light, can escape the gravitational distortion of space-time. If the Earth were to come close to one of these first, because of the intense gravitational force, parts closest to the black hole would be pulled out in a long string. This string would circle around the blackhole until it reaches close enough to the event horizon. This would continue until all of the Earth is diminished. What happens to matter after it passes the event horizon is not completly known. It is not possible to send a probe. The math talls us that matter would be squished down infinitely. What happens inside cannot be explained by theory...yet. The system deals with relativity theory (the theory of the very big) and quantum theory (the theory of the very small) both theories on their own work perfectly, but together it just does not work. This is one of the problems a "unified field theory" would explain. Some people are betting that "Super String Theory" will turn out to be that theory.