Scientists may be close to tracking down the mysterious "dark matter" that makes up more than a quarter of the universe but has never been seen.
The elusive nature of dark matter - which surrounds the galaxy in a near-spherical halo and is believed to make up around a quarter of the universe - is considered one of the most important riddles in physics.
A final identification of what makes up the enigmatic material would open up new investigations into the possibility of multiple universes and other areas, say researchers.
Members of an international team have picked up what might be the first physical trace left by dark matter using the Alpha Magnetic Spectrometer, the most sensitive particle physics spectrometer ever sent to space, now aboard the International Space Station.
The AMS studies cosmic rays - charged high-energy particles that permeate space - before they interact with Earth's atmosphere.
Of the 25 billion cosmic ray events the AMS has studied so far, "an unprecedented number, 6.8 million, were unambiguously identified as electrons and their anti-matter counterpart, positrons," CERN, the European Organisation for Nuclear Research has announced in a statement.
The head of the international research project Professor Samuel Ting says the AMS particle detector on the space station "will be able to tell us conclusively whether these positrons are a signal for dark matter or if they have some other origin".
There is still a chance the signals could result from pulsars, or neutron stars that emit electromagnetic radiation.
"There is no question we are going to solve this problem," Ting says.
Scientists are pinning their hopes on the AMS because its accuracy is "unmatched by any other experiment", says Ting, a Nobel laureate at the Massachusetts Institute of Technology.
"Our evidence supports the existence of dark matter but cannot rule out" other origins, such as pulsars, he says, adding that scientists are awaiting more data.
The findings appear in the journal Physical Review Letters.
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