We can detect dark matter by the effect that its gravity has on the visible universe. Galaxy clusters move as if they contain more mass than we can actually see. Computer studies show that galaxies are imbedded in vast halos that contain 10 times more mass than we can see-this mass is dark matter.

So what is dark matter made of? One possibility is MACHOs (Massive Compact Halo Objects). MACHOs are slow-moving chunks of cosmic material, perhaps burnt out stars, or Jupiter-sized objects, swarming in galactic halos. Or it could come from WIMPs (Weakly Interacting Massive Particles), which are fast-moving, exotic particles, left over from an earlier cosmic epoch.

So far, only a few MACHOs have been detected, but no exotic WIMPs. However, neutrinos now seem to be a promising dark matter candidate. Neutrinos are subatomic particles with no electrical charge and very little mass. They are so numerous that even with one-fifty thousandth the mass of an electron, they could account for as much matter as the entire visible universe.

Why does it matter to us?

Dark matter does matter. In fact, it could tell us whether the universe will end in a big crunch or keep expanding forever. Depending how much mass exists in the universe, there are three possible scenarios:

-If the universe has more than enough mass, gravity will eventually stop the expansion of the universe, and everything will fall back together in a ""big crunch."" This is called a ""closed universe.""
-If the universe has just enough mass, it will keep expanding forever, but at a slower and slower rate-it will never stop. This is called a ""flat universe.""
-If there is less than enough mass, the universe will expand forever, but at an accelerating rate. This is called an ""open universe.""

So far, it looks like number 3 is what will happen. Even with the mass from MACHOs, WIMPs and neutrinos, there isn’t enough mass to stop the universe from expanding forever.
Canadian Heritage Information Network
Australian Museums & Galleries Online, Australia; Centre of the Universe; Gemini Observatory, Hawaii; Glenbow Museum; The Manitoba Museum; National Research Council Canada; Planétarium de Montréal

© Canadian Heritage Information Network, 2003

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