Friday, February 19, 2010

JJNN: Dark Matter Detector

There are many mysterious things out there in the universe. Every day scientists come upon things that don't seem to fit into the grand picture as we know it now. Thanks to these things the scientists have to change the way they think about certain parts of the grand picture and our knowledge grows a little bit.

One of the things that scientists are trying to figure out at the moment is dark matter/energy. Put simply, scientists over the years have made many observations of the universe over the years and noticed that there was more stuff (matter) out there than we could see with our instruments. This effect was dubbed "dark matter." What are the effects of dark matter? Well, there are certain gravitational effects such as gravitational lensing (where a place with a lot of matter - and thus a lot of gravity - collects light from behind it like a lens) and the rotation of spiral galaxies, among other things. Scientists also think that the presence of dark matter also led to the anisotropy of the cosmic background radiation. That is why they can make beautiful maps like the one below that shows how "lumpy" the cosmic background radiation really is.

Up until this point in time there has been no way to directly see dark matter. This means we don't really know what it is made up or even if it actually physical matter at all. It could be that if we find out exactly what dark matter is made out of and how it is formed we could find a key to a great amount of knowledge this universe. That is why there are many groups looking to build dark matter detectors. One of those groups is from Tokyo University (even though it is based in Gifu). You can see a picture of their partially completed detector below.

The detector is actually a 1 meter across ball of 60 smaller detectors. The team has dubbed the smaller detectors XMASS. XMASS stands for "Xenon detector for Weakly Interacting MASSive Particles." I don't know about you, but I think they really cheated in their acronym to make the detector sound cool. Technically it should be XDWIMP. I think I like XD-WIMP better than XMASS. I reason I like XS-WIMP better is because WIMPs are exactly what this detector is looking for. By WIMP I don't mean a weak person, I mean particles that probably exist, but are so weakly interacting with normal matter that we have no real way of detecting them. WIMP stands for weakly interacting massive particle.

So, if these particles do not really interact with other particles how do we detect them? That very question has been plaguing scientists that do actually want to detect these particles. The XMASS detectors are filled with liquid Xenon which is as cold as -100C (-148F). Almost all of the WIMPS that pass though the detector do not interact with the xenon, but the ones that do will give a little energy to the liquid. This energy is then again released in the form of light. This light can be detected by the photo sensors on the inside of the detectors. One flash of light equals one WIMP that interacted with the liquid.

This actually leads to a problem. There are a lot of other things that could interact with the liquid to give it energy. Things like high energy particles from the sun or high energy particles that are zooming around the universe. So this leads to the problem that they have to find a way to shield the detectors from these other particles and energies. They do this by basically putting the detector at the bottom of a huge hole. The earth itself (along with some water) will shield the detector from background radiation.

It will be exciting to see what comes out of this detector and what kind of discoveries can be made. I hope it goes a lot smoother than a some other experiments, like the LHC.

Any way, it is now time for the word of the day. Today's word is 暗黒物質(あんこくぶっしつ). It is pronounced ankoku busshitsu and it means dark matter. I wonder what kinds of scientific strides ahead can be made when we figure out just what dark matter is.

See you next time at JJNN

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