conceptFEATURED CONCEPT: Dark Matter
Unlike ordinary matter, dark matter does not emit or absorb light--or any other type of electromagnetic radiation. Consequently, dark matter cannot be observed directly using a telescope or any other astronomical instrument that has been developed by humans. If dark matter has these strange properties, how do we know that it exists in the first place?
Like ordinary matter, dark matter interacts gravitationally with ordinary matter and radiation. Astronomers study the distribution of dark matter through observing its gravitational effects on ordinary matter in its vicinity and through its gravitational lensing effects on background radiation. The background image shows the bullet cluster, a famous example where the visible matter does not follow the mass distribution.
Combining all the available evidence, dark matter represents about 83% of the matter content of the universe. Read more about dark matter on this web page. Let us know your questions and comments on the message board.

User profile Profile Teco
Born 1938. Physics professor in Havana, Cuba, immigrated to USA in 1970 because of philosophical and political disagreements with the Communist...

Beta testing
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