New Research: We Live in a Cosmic Cave Full of Dark Matter

Experimental results released last month from Italy’s deep underground XENON100 detector revealed, sadly,

no dark matter

, at least in its most commonly theorized form (weakly interacting massive particles, or WIMPs). It was a blow for sure, but the experiment, housed in the Gran Sasso labatory in the heart of a mountain 120 km from Rome, isn’t the final say in the dark matter hunt by any means. There are actually a dozen different direct detection experiments underway right now, all across the world and all underground (to help block out background cosmic rays), the most recent of which is the

LUX

dark matter detector being constructed nearly a mile below the surface in an abandoned South Dakota mine, which will up the detection sensitivity threshold by several orders of magnitude. Given the many, many brains currently working on the direct detection problem, today’s publication of a new

study

in the journal

Monthly Notices of the Royal Astronomical Society

finding, indirectly, more dark matter around the Sun than previously thought should deliver some hope.

So, let’s recap dark matter real quick. In the 1930s, Swiss astronomer Fritz Zwicky noted that the observed movements of galaxies weren’t adding up. There was something invisible there exerting a gravitational force, a very large something. Right about the same time, Jan Oort in the Netherlands discovered that there was a much higher density of matter around the Sun than could be explained by all of the observable stuff (gases and stars). The explanation for the disparities became what we now call dark matter, a theorized ghostly something that makes up most of the matter in the universe, yet interacts hardly at all with the observed universe beyond gravity. While we observe it fairly easily in the movements of galaxies, the global race is still on to detect it directly.

The astronomers behind the new study, based at the University of Zürich, the ETH Zurich, the University of Leicester, and NAOC Beijing, used mass-measuring techniques based on new state-of-the-art galaxy simulations to come up with results showing not just dark matter hanging out around the Sun, but more dark matter than previously thought. It’s good news for the small army of researchers working on direct detection; our old measurements were wrong, but wrong in the direction of underestimation.

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"We are 99 percent confident that there is dark matter near the Sun," says the study’s lead author, Silvia Garbari. "In fact, our favored dark matter density is a little high. There is a 10 percent chance that this is merely a statistical fluke. But with 90 percent confidence, we find more dark matter than expected. If future data confirms this high value, the implications are exciting. It could be the first evidence for a 'disc' of dark matter in our galaxy, as recently predicted by theory and numerical simulations of galaxy formation. Or it could be that the dark matter halo of our galaxy is squashed, boosting the local dark matter density."

The idea is that dark matter consists of a new particle. The new particle doesn’t totally ignore the “light” matter in the universe, but, generally, it sails around unimpeded. Which means it should be one of the only things sailing through the rocks deep underneath South Dakota, where we’ll be looking for dark matter particles to occasionally crash into the nucleus of a xenon atom floating around in a giant tank full of nothing but supercooled pure liquid xenon. That collision will kick off a few photons, which should then be detected by one of 122 photomultipliers located around the tank. This should happen a whopping handful of times a year.

“If dark matter is a fundamental particle, billions of these particles will have passed through your body by the time you finish reading this article,” the new study’s co-author George Lake adds. "Experimental physicists hope to capture just a few of these particles each year in experiments like XENON and CDMS currently in operation. Knowing the local properties of dark matter is the key to revealing just what kind of particle it consists of."

Reach this writer at michaelb@motherboard.tv.

Connections:

• What the Fuck is Dark Matter
• Why Our Dark Matter Ghost Hunting Expeditions Might Be Failing
• Trapped Under Ice: Looking for Dark Matter in Antarctica