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Black
Holes
Black holes are one of the greatest mysteries of space. We cannot see them,
and astronomers only know they exist because of their effect on nearby
stars. They happen sometimes after a star blows up in a supernova. The
star’s gravity pulls all of the material that remains after the explosion
inward, squeezing it smaller and smaller. Either a tiny neutron star forms
or a black hole- an object with such strong gravity that nothing can escape,
not even light.
The
gravitational force is so very strong near the black hole because all of
its matter is located at a single point in its center. This point is called
a singularity. It is believed to be far smaller in size than the nucleus
of an atom. Most astronomers believe the Milky Way galaxy- the galaxy in
which the Earth is located- contains millions of black holes. No one has
discovered a black hole for certain.
However,
astronomers have found strong evidence for seven black holes in the Milky
Way galaxy and a nearby galaxy. There are two types of black holes- rotating
and nonrotating. Both have a spherical surface called an event horizon
from which nothing can escape. Once an object passes through an event horizon,
it disappears from our universe forever.
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