A small step toward dark matter

The entire universe in blog form
Oct. 21 2008 12:30 PM

A small step toward dark matter

Dark matter -- the mysterious stuff that doesn't emit light, and doesn't appear to interact with normal matter much if at all -- outmasses normal matter in the Universe by a comfortable amount. We know it's out there, and we even have a decent grasp of what it's doing, but, maddeningly, we don't know what it is.

We know what it isn't. It isn't cold gas, or dead stars, or rogue planets (seriously), or mini black holes. There's a long list of things it might be, and most of those items have been checked off. All that's left are weird particles that are only theoretical. We think they might exist, but our particle detectors and accelerators haven't turned them up yet.

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  


People are trying, though! In the LHC there is a special detector set up to look for dark matter. There are also other detectors spread out around the world looking for some sort of interaction of dark matter with normal matter.

Update: in this next paragraph, I originally had mistaken the Picasso group doing this work with the entire Observatory; I was corrected in the comments so I have fixed this paragraph.

One such detector is in Canada. Or, rather, below it. The Sudbury Neutrino Observatory is an astronomical observatory located over a mile underneath the Canadian landscape. Shielded by solid rock, detectors there are designed to look at subatomic particles from space such as neutrinos, ghostly particles created during some particle interactions. In fact, a detector at SNO was crucial in solving the Solar Neutrino Mystery.

Now it turns out they may help solve the dark matter mystery as well! Basically, the Picasso group at SNO is trying to detect one kind of proposed dark matter particle (a weakly interacting massive particle, or WIMP). The problem is, the signal from such a particle looks a whole lot like the signal they get from an everyday alpha particle -- the nucleus of a helium atom, which is a common radioactive decay product. Differentiating between the two is really, really hard.

However, scientists with Picasso now think they've figured out a way to distinguish them:

"When we looked at our calibration data taken with neutrons and compared them with our alpha background data we saw a peculiar difference which we attributed first to some detector instabilities or gain drifts in our electronics," said experiment spokesperson Viktor Zacek of the University of Montreal in a statement.

"However when we checked the data and refined the analysis the discrimination effect became even more pronounced," he said.

It's like trying to hear a friend (a WIMP) talking to you in a noisy bar, when someone else with a similar voice (an alpha particle) is shouting next to you. This new technique will allow scientists to essentially filter out the similar voice, allowing them to hear their friend's voice.

While this isn't an actual detection of a dark matter particle, it's a nice solid step in that direction. Remember, scientific progress isn't usually just waking up one day and realizing you've overthrown the leading paradigm. It's usually a series of small progressions, a journey of a thousand steps. Each movement forward is important, and when taken in total, they take you along the path to your goal: understanding the Universe. Lots of people say it's not the goal, it's the journey that's important. While I think this goal is pretty important, in this case the journey itself can be cool, too.

Tip o' the axion to BABloggee sooz.



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