No, I'm not trying to be insulting. That stands for Weakly-Interacting Massive Particles, and these are usually what astrophysicists are talking about when they bring up 'dark matter'. However, there may be another kind of dark matter, which could actually form an entire 'dark world' around us that we wouldn't even know exists.
Dark matter is called 'dark' because we can't see it. It doesn't emit any radiation. However, scientists figure that something has to be there, to account for how the universe expanded, and how it moves and behaves. Apparently, there's even more dark matter in the universe than the normal matter that we see all around us. In fact, of the total sum of all the matter in the universe, normal matter only accounts for less than 15% of it, with dark matter making up the rest. So, learning about what dark matter is, and where it comes from, and what effect it has on us and the matter we see is pretty important.
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Dark matter particles are called WIMPs because they are particles with mass (and thus they create gravity), and they only interact through something called the 'weak force', which is what makes radioactive elements decay (among other things). They don't emit electromagnetic waves that we can detect, and they don't seem to react to the 'strong force' (the one that holds atomic nuclei together), but according to Andrey Katz of Harvard University's Center for the Fundamental Laws of Nature, that doesn't necessarily have to be true of all dark matter.
"There is no good reason to assume that all the dark matter in the universe is built out of one type of particle," Katz told SPACE.com.
It might be that dark matter can only affect normal matter through the weak force and gravity, and there may be a 'dark electromagnetism' and 'dark strong force', so that there could be 'dark atoms'. This type of dark matter could be just as abundant as normal matter (with WIMPs making up the rest).
Katz and his colleagues at Harvard wrote a paper published last month that talked about the possibility that galaxies may have more than one disk of matter — one of normal matter that we can see, and a second 'dark disk' made up of dark matter.
This new type of dark matter may give us more places to look for the elusive stuff, too.
There have been efforts to detect dark matter already, not by seeing it directly of course, but by seeing its effect on normal matter. An experiment put in orbit, outside the International Space Station, turned up some interesting results back in April as it looked for the particles that may be seen from dark matter colliding with normal matter. Astronomers have also been trying to find dark matter's effects in gravitational lensing, where regions of space we know to be empty of normal matter may still form gravity wells that act as giant lenses in space, magnifying our view of whatever is on the other side them.
New methods would be to watch for how these bigger, slower dark atoms interacted with normal matter.
There's also the Gaia Space Observatory, which is being launched by the European Space Agency later this year. It's mission will be to map out the movement of all the stars in the galaxy, and according to Katz: "This is how we might first detect this dark disk."
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Is there a whole new 'dark universe' around us that we haven't been able to see yet? If these dark particles can form dark atoms, they may have dark chemistry and may emit dark radiation. There could even be dark stars, dark planets and dark life. Maybe dark matter and dark energy will turn out to be a shadow of an alternative universe (or multiple alternate universes) onto our own. The possibilities are fascinating to explore.
(Photo courtesy: Bruno Gilli/European Southern Observatory)
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