Scientists throw light on 'dark matter'

 An international team of scientists on Wednesday announced what appears to be the first evidence in support of the elusive “dark matter,” which constitutes the bulk of the universe, but skipped detection so far.

Unusual data on the presence of a sub-atomic particle called “positron" in space collected by an instrument fitted to the International Space Station gives scientists an indication on the existence of dark matter. The evidence, however, is not conclusive yet.

“Over the coming months, the Alpha Magnetic Spectrometer on-board ISS will be able to tell us conclusively whether these positrons are a signal for dark matter, or whether they have some other origin,” Nobel laureate Samuel Ting, who headed the team, said at a conference in Geneva on Wednesday. The results will be published in the journal “Physical Review Letters.”

Cosmic rays are charged high-energy particles that permeate the space. The experiment was designed to study them before they interact with the earth’s atmosphere.

An excess of antimatter - opposite of matter - within the cosmic ray flux was first observed around two decades ago. The origin of the excess, however, remains unexplained.

One possibility, predicted by a theory known as supersymmetry, is that positrons could be produced when two particles of dark matter collide and annihilate. The theory predicts the observations made by AMS.

The AMS measurement, however, can’t yet rule out the alternative explanation of the positrons originating from pulsars distributed in the galaxy.

The results are based on some 25 billion recorded events, including 400,000 positrons with energies between 0.5 GeV and 350 GeV (Giga electron Volt), recorded over a year and a half. This represents the largest collection of antimatter particles recorded in space.

“When you take a new precision instrument into a new regime, you tend to see many new results, and we hope this will be the first of many,” said Ting. “AMS will allow us to tell whether our current positron observation has a dark matter or pulsar origin.”

Supersymmetry theories also predict a cut-off at higher energies above the mass range of dark matter particles, and this has not yet been observed. In the coming years, the AMS is expected to further refine the measurement and clarify the unusual behaviour of positrons seen at energies above 250 GeV.