… dark matter is a hypothetical form of matter of unknown composition that does not emit or reflect enough electromagnetic radiation to be observed directly, but whose presence can be inferred from gravitational effects on visible matter.
Much of the evidence for dark matter comes from the study of the motions of galaxies. Many of these appear to be fairly uniform, so by the virial theorem the total kinetic energy should be half the total gravitational binding energy of the galaxies. Experimentally, however, the total kinetic energy is found to be much greater: in particular, assuming the gravitational mass is due to only the visible matter of the galaxy, stars far from the center of galaxies have much higher velocities than predicted by the virial theorem.
I think it’s amazing that science can infer the existence of an untraceable particle by observing the ancient movements of massive clusters of stars. Personally, I can’t even figure out how to close Tupperware containers, so: kudos, science.
they were just talking about this on npr…sortof…the part where they interview Neil de Grasse Tyson is rally interesting.
http://www.wnyc.org/shows/radiolab/episodes/2006/05/12