In DepthParticle Astrophysics

Space magnet homes in on dark matter clue

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Science  08 Feb 2019:
Vol. 363, Issue 6427, pp. 572-573
DOI: 10.1126/science.363.6427.572

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A costly and controversial space-based cosmic ray detector has found possible signs of dark matter, the invisible stuff thought to supply most of the universe's mass. Or so says Samuel Ting, a Nobel Prize–winning particle physicist at the Massachusetts Institute of Technology in Cambridge and leader of the Alpha Magnetic Spectrometer (AMS), which is perched on the International Space Station (ISS). In 2014, AMS researchers reported an unexpected flux of positrons above a certain energy, which could come from dark matter particles colliding and annihilating one another to produce electron-positron pairs. Now, with three times as many data, AMS researchers have shown that the excess falls sharply at slightly higher energy. That cutoff could be further evidence of dark matter collisions, as the dark matter particles' mass would limit the positrons' energies. However, the positrons could also come from a pulsar or, some cosmic ray experts say, even the interactions of cosmic rays themselves. And time may be running out for the AMS. It narrowly avoided the budget ax a year ago, but this October astronauts are scheduled to perform a spacewalk to repair the 8500-kilogram detector. Even if the AMS runs until the ISS shuts down, perhaps in 2024, it may never collect enough data to resolve the issue.