What is dark matter, and what are the problems with it?
Dark matter is any stuff in the universe which we can tell exists but can't see. This means the material is not giving off light which we can see, but we can measure its gravitational effect on other objects in the universe.
In the 1930's, astronomer Fritz Zwicky discovered that the mass of visible material in a cluster of galaxies was much less than the total mass of the cluster should have been. It seems 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. They are usually too faint to be detected except for by their gravitational effect. Other dark matter may be in the form of exotic particles and black holes. Stay tuned to 'The Universe' for more on dark matter.
Submitted by Ron (age 28, Israel)
(March 13, 1998)
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