An international team of researchers announced in Switzerland on Wednesday that an experiment on the International Space Station may have seen hints of something called dark matter. The finding could be a milestone in the decades-long search for the universe's missing material.
Only a tiny sliver of stuff in the universe is visible to scientists; the rest is dark matter. Researchers don't know what it is, but they know it's there. Its gravity pulls on the things we can see.
"We live in a sea of dark matter. Our galaxy is embedded in a huge roughly spherical halo of dark matter particles," says Michael Salamon, who is with the U.S. Department of Energy.
Salamon, who was part of the team behind Wednesday's announcement, says that dark matter is beyond anything predicted by current scientific theories.
"What that means is, if we detect dark matter and learn something about its nature, we will have made a major impact to our understanding of physics and nature itself," he says.
That's a big part of why scientists from 16 countries spent $2 billion building a detector designed to pick up any hint of this mystery material. Their Alpha Magnetic Spectrometer was carried into space two years ago and bolted onto the side of the International Space Station.
Researchers announced Wednesday the AMS has detected a large number of high-energy particles, which could be coming from collisions of dark matter. Theories suggest that when dark matter particles smash together, they annihilate one another. The enormous energy released creates visible particles, and it's these particles that might be showing up in the detector.
Sam Ting, a Nobel Prize-winning physicist who is responsible for the AMS, says this is only the beginning. As the AMS collects more particles, it should be able to tell whether they are coming from dark matter collisions.
"I think with AMS there is no question, we are going to solve this problem," he says from Geneva.
But other scientists have doubts about whether the project really is seeing dark matter.
"I would bet against dark matter being the origin of these particles at this time," says Dan Hooper, a scientist at the Fermi National Accelerator Lab in Illinois.
It's possible the particles they have seen could have come from somewhere else. Gregory Tarle, a physicist at the University of Michigan, saw similar particles in an experiment he ran years ago.
Tarle says that the remains of certain dead stars can hurl the same kinds of particles into space. A nearby star like this could be the source of the particles the AMS has seen.
"The problem with all these type of measurements is that they are not definitive for the discovery of dark matter annihilation," he says.
Ting says more data should help, and the experiment does have time on its side. It is expected to continue recording particles as long as the International Space Station is operating — currently until 2020.