Astronomers have no idea what dark matter is, but they have a few guesses. Since they can’t see the stuff directly, they’re trying to chip away at what it can’t be, peeling away theory after theory. Eventually, there should be a few theories that have withstood the most experiments, and best model what astronomers see out in the Universe. Physicists at Fermilab have made one of those steps forward, constraining the characteristics of dark matter, and overturning a recent discovery… by not seeing anything unusual.
We can’t see dark matter, but we know it’s out there. Galaxies should spin themselves apart but they don’t thanks to being inside a halo of dark matter. Amazing images from the Hubble Space Telescope show dark matter’s gravitational distortion on the light from distant galaxies. Oh, it’s out there all right.
So what is it?
Astronomers have two theories. One is that their ideas about gravity are wrong. By modifying our understanding of how gravity works over large distances, you can remove the need for dark matter entirely.
The other possibility are “weakly interacting massive particles”. These are actual particles, made of “something”, but we can’t see them or detect them in any way except through their pull of gravity.
Particle physicists have been searching for dark matter particles using powerful atom smashers, just like they discovered all the sub-atomic particles they’ve found so far.
A new experiment at the US Department of Energy’s Fermi National Accelerator Laboratory announced this week that they’ve made some headway in this search. According to theories, when dark matter particles interact with regular matter, it’s different from the way regular matter interacts. The Fermilab experiment has ruled out one of the last possible ways that the theories have predicted this should happen.
Their experiment, called COUPP, uses a glass jar filled with a litre of iodotrifluoromethane (a fire-extinguishing liquid known as CF3I. As particles strike the CF3I, it causes tiny bubbles to form in the liquid. The scientists can detect these bubbles as they reach a millimetre in size. By watching the interactions, researchers should be able to know if they’re coming from regular matter or dark matter.
So far, their results contradict another search called the Dark Matter experiment (DAMA) in Italy, who claimed to see dark matter interactions. The results for the DAMA experiment predicted that COUPP should have found hundreds of dark matter interactions, but they didn’t see any.
This research appears in the February 15th issue of the journal Science.
Original Source: Fermilab News Release