DARK ARTS: Astronomers using the W. M. Keck Observatory, the Hubble Space Telescope, and other telescopes on Mauna Kea have studied a giant filament of dark matter in 3D for the first time. Image released Oct. 17. 2012. Image: Image by ESA; additional elements by K. Teramura, Univ. Hawaii Institute for Astronomy
The hiding spots for the particles making up dark matter are narrowing, and the answer to this cosmic mystery could come within the next three or four years, scientists say.
Dark matter is an elusive substance that is invisible and almost never detected, except by its gravitational pull. Yet astronomers say it likely makes up a quarter of the entire universe and dwarfs the amount of normal matter (galaxies, stars and planets) out there in space.
Just last week, particle physics discovery from the Large Hadron Collider in Switzerland cast doubt on a theory called supersymmetry, which predicts the existence of particles that are among the leading candidates for dark matter. That finding limited the types of supersymmetric particles that can exist, but didn't take the supersymmetry explanation off the table completely.
And supersymmetric particles are just one of a number of theorized particles that might account for dark matter. Searches for these and other undiscovered particles have been underway for decades, though none have been detected so far. [Twisted Physics: 7 Mind-Blowing Findings]
"I think we're looking in enough different ways that unless it's something that we just haven't thought of at all yet, it seems to me we're very likely to find it within the next decade," said Dan Bauer, a physicist at the Fermi National Accelerator Laboratory in Illinois working on one of the experiments, called CDMS.
Dark matter on the run
The leading experiments aimed at detecting dark matter are just starting to operate at sensitivity levels thought to be sufficient to detect signals from these particles, and their results should be in within about three or four years, Bauer said.
"If we don’t find it in this next round of experiments, I think everyone will be a bit discouraged," Bauer told SPACE.com.
To be dark matter, the potential particles must all be neutral and stable, and interact very rarely with other types of matter.
Most of these fall into a category of heavy particles called weakly interacting massive particles (WIMPs). WIMPs are predicted by supersymmetry, posits the existence of heavier partner particles for all the known particles in the universe with the same electric charge but different spin. [NASA's Quest for Dark Matter (Video)]
Several experiments are underway to search for WIMPs by placing large masses of material, such as xenon or germanium, deep underground and shielded by many layers of protection aiming to keep all other particles out. If any particles do make it past these barriers and collide with the atoms in the xenon or germanium, they will very likely be WIMPs, the thinking goes.
CDMS (which stands for the Cryogenic Dark Matter Search), started in a tunnel underneath Stanford University in California, and a newer, more sensitive version of the project is now underway even deeper underground in Minnesota's Soudan Mine.
Another WIMP-hunting experiment is called XENON100, the latest iteration of a search based at the Gran Sasso underground laboratory in Italy. And a new project called LUX (the Large Underground Xenon experiment) under construction at the Homestake mine in South Dakota could be a big player, too.