Trapped Under Ice: Looking for Dark Matter in Antarctica

Almost everyone in astronomy has the utmost confidence in this thing called dark matter: it explains how galaxies behave, temperature fluctuations in the Cosmic Microwave Background, and a number of related things too technical to explain here. It’s out there and has a huge impact on the universe and, generally, how the universe is like it is enough for us to exist. In a way it’s like the Higgs boson:a key to our models of the universe, but a key we haven’t actually seen in a lab.

This is probably a lot more frustrating to know-nothings like us that don’t get the complex math involved in everything, but science is still science and needs to see it firsthand. Dark matter doesn’t get quite the attention the Higgs hunt does, but that shouldn’t be because the search methods are any lamer than colliding particles in a big tube. Most famously, the hunt for dark matter has gone down deep in a defunct Minnesota mine; the goal is to get as far away from normal radiation as possible to prevent interference.

Another way we might be able to find the stuff is through indirect detection, looking for its byproducts. One of these byproducts is thought to be a particle called the neutrino, created along with photons when neutralinos, the supposed dark matter particle, annihilate. Enter IceCube, a neutrino telescope one kilometer large on a side and deep in the ice under the South Pole. That ice is stunningly pure, creating a natural observatory that blocks out most interference, but allows neutrinos to travel through.

When those neutrinos hit an oxygen atom, they finally give us something we can see. From a piece in Fermilab’s Symmetry Breaking magazine today covering the experiment’s long history:

Like many other neutrino detectors, IceCube uses photomultiplier tubes to peer through a clear medium, looking for faint streaks of blue Cherenkov radiation—shockwaves from particles that are moving faster than light can travel in that medium. Most of what any such detector sees is background, but occasionally an energetic neutrino collides with an atomic nucleus and produces a muon headed in the same direction—the main quarry in the hunt for neutrinos from beyond the Sun.

Researchers get only a few months a year when the South Pole is accessible via airplane. So far, just based on data collected during its construction, IceCube has delivered enough information to form a map of the neutrino sky and given researchers a good idea of the maximum amount of dark matter that could be lurking in our own Sun (still plenty). UC Berkley’s Spencer Klien says simply that we can expect a “bountiful physics harvest” to come.

There’s almost certainly a The Thing joke in here, but damned if I can find it. Apologies.

Reach this writer at michaelb@motherboard.tv.

Image: icecube.wisc.edu.