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a r k M a t t e r
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Dark
matter may sound very mysterious, but it is simply a name which astronomers
give to any stuff in the universe which we can detect gravitationally
but not "see". In other words, for many possible reasons,
the material is not emitting light of any wavelength which we can
detect, but we can measure its gravitational effect on other objects
in the universe.
The first evidence of dark matter was
found in clusters of galaxies back in the 1930's. Astronomer Fritz
Zwicky discovered that the mass of luminous material in a cluster
of galaxies (i.e. the galaxies themselves and any gas which was detected)
was much less than the total mass of the cluster implied by the velocities
of the galaxies. Evidence of dark matter has since been found within
galaxies, and it appears that more than 90% of the total mass of the
universe may be dark matter.
The search for dark matter continues.
Some dark matter is in the form of 'brown dwarfs', 'black dwarfs',
and planets, which we know exist but which are generally too faint
to be detected other than by their gravitational effect. It seems
unlikely, however, that these dim objects can account for all of the
missing mass. There are many other candidates, ranging from as yet
undetected exotic particles to black holes. Stay tuned to 'The Universe'
for more on dark matter. |
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