How Do Black Holes Form?
Slide 11 of 22
It is unlikely that we will be able 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.
There have however been suggestions recently that certain types of microscopic black holes can be made by smashing heavy ions together in particle accelerators. Such suggestions depend critically on some as yet speculative assumptions about the nature of gravity at the microscopic level. It will be interesting to see whether these conjectures can be realized.
Nature, on the other hand, seems to have not difficulty making black holes. 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 there is considerable evidence for the existence of black holes at the center of most galaxies, including our own.