A small percentage of the particles that hit the detector are unusual things called positrons, which are like electrons but with the opposite charge. They're in the class of particles known as antimatter.
There's not much antimatter in our universe, and there hasn't been for many billions of years. When matter and antimatter collide, they are mutually annihilated. The universe early in its history had a bit more matter than antimatter, an asymmetry that, from the human standpoint, is fortuitous, because matter and antimatter in precisely equal amounts would have obliterated each other and left a starless, planetless, uninhabitable cosmos.
Physicists say rare antimatter particles, such as positrons, can be created in certain violent, high-energy environments. For example, positrons might have been flung into space from the atmosphere of a pulsar, an ultra-dense, rapidly rotating star with a powerful magnetic field.
Another theorized source of positrons is dark matter. If antimatter seems exotic, dark matter is even more so. No one has ever seen the stuff, and its existence has never been nailed down definitely. Dark matter emits and absorbs no light, and interacts with ordinary matter in a ghostly fashion, primarily through gravity. Dark matter is thought to affect the way galaxies move; they rotate in a manner that suggests that they are carrying some unseen load. In the past two decades, other experiments and detectors have bolstered the idea that dark matter is far more abundant than ordinary matter.
The surprising abundance of positrons has been established by earlier experiments. But the AMS has "unprecedented accuracy and sensitivity," Ting said when questioned by a reporter about whether the mission was worth the cost.
Although most of his statements were cautious, under questioning, he said his data "support" the dark matter origin of the positrons. He reiterated that he cannot rule out the pulsar origin.