I find the subject of dark matter very interesting. Just a question to chalnoth, do we have a model of what dark matter actually is?
Im aware of detecting it through gravity but I was unaware of other methods of detecting it, could these indicate what other properties it posseses?
Well, the problem is we have too many models for what dark matter might be. Right now we have four basic limitations on the properties of dark matter:
1. It has to explain the halos of invisible, weakly-interacting matter in which galaxies sit.
2. It has to explain the CMB anisotropy pattern (this forces the dark matter to be made up of massive particles...eliminating the possibility for it to be made up of neutrinos, the only weakly-interacting particle we know of today, because neutrinos are too light).
3. It has to have properties which allow it to be created in the exact right amounts in the early universe.
4. It has to be weakly-interacting enough that we won't have seen it with the experiments designed to date.
Right now, there are a number groups attempting a number of different ways to discover dark matter. Scientists in particle accelerators are looking for missing mass (this would be a signature of a massive, weakly-interacting particle whose properties could be measured by observing the particles which the detectors do detect). There are a number of underground experiments searching for weakly-interacting particles that pass through the Earth in tremendous numbers. Some groups are looking for decays or annihilations of dark matter particles by searching the skies for the products of such events.
There are others, too, but this is just what I can remember off the top of my head.
As for the models, right now supersymmetry, which describes a unification between the strong, weak, and electromagnetic forces, and is also a component of the vast majority of string theory models, provides the inspiration for most dark matter candidates.
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