Slide 6 of 13
It is impossible to manufacture black holes in the laboratory. The density of matter
required is too great. In order to make a black hole the size of a baseball, you would
have to pack all the matter in and on the Earth into a volume the size of my fist.
This is much greater than the density of nuclear matter, for example.
Nature can make black holes, however. Gravity is always attractive. Matter naturally collapses unless there is some other force to hold it up. The objects in this room are
kept from collapsing by electromagnetic forces. The gas in an active star is held up
by thermal pressure. However, once a star uses up its thermonuclear fuel, it starts to
collapse, and if there is enough mass to overcome other, microscopic forces, it
invariably collapses into a black hole.
Stars in galaxies also collapse, and as we will see there is evidence for black holes
at the center of most galaxies, including our own.
