How do black holes form?
nWe can make them in
the lab !?
nFrom the collapse
of burn-out stars.
nGravitational
collapse at galactic cores.
| 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. |
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