New results from the particle detector attached outside the International Space Station show something else beside ordinary matter is generating cosmic rays, the lead researcher said Tuesday.
More cosmic ray detections are needed before scientists will know for sure if they're seeing telltale fingerprints of dark matter colliding or if they've found particles generated by highly magnetized, rotating neutron stars known as pulsars.
"We know something new has happened, but we still do not know the origin," Massachusetts Institute of Technology physicist Sam Ting, lead researcher of the 600-member Alpha Magnetic Spectrometer science team, said at a space station research conference in Chicago.
"In a short time, we'll really be able to resolve the mystery," he said.
Unlike visible or ordinary matter, dark matter cannot be directly detected by electromagnetic radiation. Yet scientists believe its gravity is responsible for keeping the galaxy -- and the universe for that matter -- together.
Dark matter and its even stranger, anti-gravity cousin, dark energy, which is credited with speeding up the universe's expansion, comprise about 95 percent of the known universe.
Since being installed on the station in May 2011, the AMS particle detector has logged 50 billion cosmic ray hits and relayed information about their energy, direction and contents to physicists for analysis.
Of particular interest is how many positrons -- the antimatter counterpart to electrons -- are detected relative to the overall number of positrons and electrons. Last year, the AMS team reported a proportionally higher number of positrons, though there was not enough data yet to see if the ratios reconciled at higher energy levels, a possible sign of dark-matter collisions.
"The rate of the increase and where you cut off depends on the mass of dark matter," Ting said.
The new data show the ratio of positrons to the total population of electrons plus positrons has "changed its behavior from increasing, to becoming energy independent," Ting wrote in an email to Discovery News.
"This increase indicates it cannot come from ordinary cosmic ray collisions," Ting said.
"We have also measured the positron flux accurately," he added. The flux increases up to 10 billion electron volts of energy, flattens out at up to 35 billion electron volts and then increases again," Ting said.
"These two behaviors show that the origin of positrons in the cosmos is quite mysterious," he added. "It is too early to say they are definitely from dark matter."