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Black holes were first predicted by Albert Einstein in his theory
of general relativity. In principle, a black hole is a single
point of matter so dense that nothing can escape its gravitational
field. The common science fiction image of a vast hole which ‘sucks’
everything into itself like a vacuum cleaner is not accurate.
Black holes are thought to be the remains of very large stars
which have collapsed upon themselves. As the matter is compressed
upon itself, its gravitational energy increases, causing it to
collapse upon itself still further. When all the matter is condensed
to a single point, a black hole results.
Black holes cannot be observed by normal methods, because not
even light can escape from its gravity. There is strong evidence
to support their existence, however. Matter circles around black
holes in accretion disks of particular sizes and shapes. Furthermore,
some astrophysicists believe that black holes of certain sizes
emit x-ray radiation.
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