Scientists have found an abundance of highly energetic antimatter particles originating from space that could be a flag marking the existence of dark matter.
If confirmed, the discovery would be the closest scientists have come to success in their search for this elusive, invisible material that is thought to make up much of the universe.
Researchers have been using the Alpha Magnetic Spectrometer mounted on the International Space Station to observe cosmic rays and look for the signatures of dark matter and antimatter. In a forthcoming paper in the journal Physical Review Letters, an international team of researchers describe how they found extra antimatter particles, particularly positrons in the cosmic rays headed toward Earth – a possible dark matter signature.
The theory of supersymmetry predicts that two dark matter particles colliding would produce positrons -- the antimatter counterpart of electrons. However, there’s also the possibility that the positrons originate from strongly radiating neutron stars called pulsars.
“Over the coming months, AMS will be able to tell us conclusively whether these positrons are a signal for dark matter, or whether they have some other origin,” spokesman Samuel Ting said in a statement released by CERN.
Dark matter earned its name thanks to the fact that it does not interact with light, or emit any significant amount of electromagnetic radiation. This makes looking for it extra-tricky. Most of what we know about dark matter comes to us indirectly, through how it affects other matter and radiation via gravitional forces.
Scientists actually first stumbled upon dark matter when they realized that galaxies were spinning too fast to hold together, given what we knew about their masses. All the stuff we can see -- interstellar dust, planets, and stars -- didn't have enough mass to generate the gravitational force necessary to keep the galaxies from flying apart as they spun. Dark matter is one of the better solutions to explain the discrepancy; there's a lot of mass that's just gone unnoticed until now.
Most current models show that we live in a sea of dark matter. Occasionally the particles that make up dark matter -- weakly interacting massive particles, or WIMPs, will come into contact with ordinary matter, and scientists might be able to see signs of that interaction. There are two methods for trying to spot WIMP interactions on Earth: either with particle accelerators, or by using detectors in labs deep underground, shielded from cosmic radiation. But neither of these methods has yielded any significant evidence thus far.
Space seems to be the more promising route in the quest for dark matter. At a NASA briefing on Wednesday, Ting said that the forthcoming paper represents just a tenth of the data AMS has gathered thus far. While other experiments have detected similar positron signatures, AMS is a more sophisticated machine that can examine the cosmic ray spectrum to a much finer resolution.
Even so, there is still the possibility that dark matter does not exist. Some scientists have proposed that tweaking our descriptions of gravity could explain the galaxy spin conundrum, though such a solution could make things even more complicated for physicists.
At the NASA briefing, one reporter asked how long it could be before definitive proof of dark matter was discovered.
"It doesn’t depend on us; it depends on nature," Ting said.