The Search for Dark Matter
It seems the universe is made of more than meets the eye. Two clues from astronomy have led physicists to suspect that a type of invisible matter, which they call dark matter, makes up part of the mass of each galaxy.
When researchers measured the masses of all the stars and planets in neighboring galaxies, they discovered that the gravity of those objects alone would not be great enough to hold them together. Something they could not see must have contributed mass and therefore gravitational pull. Second, they observed in what seemed to be empty space distortions of light that only large masses can cause.
Now physicists posit that 23 percent of the universe is composed of dark matter, compared to just 4 percent made up of visible matter and 73 percent made up of dark energy. But no one has observed dark matter directly. The MAX collaboration is engineering two multi-ton detectors filled with noble liquids that will be able to detect the mysterious particles. One will contain liquid argon and the other liquid xenon.
Theories of supersymmetry predict that dark matter exists in the form of undiscovered weakly interacting massive particles, or WIMPs, formed in the early universe and subsequently clustered in association with normal matter. Scientists hope to detect WIMPs by building large detectors and waiting for dark matter particles to leave a tell-tale signal by colliding with the nuclei of the atoms inside.