Michael Lucy
A China-led satellite mission has detected an anomaly in cosmic ray signals that may indicate the presence of dark matter, the mysterious stuff astrophysicists believe constitutes as much as 80% of the mass in the universe.
In a report published in the journal Nature, scientists from the DArk Matter Particle Explorer (DAMPE) project, based at Purple Mountain Observatory in Nanjing, deliver the most accurate and detailed measurements yet of high-energy cosmic ray electrons and positrons (CREs) bombarding the Earth from outer space.
CREs are produced by the usual astronomical suspects, such as supernova explosions, but some theories suggest that they may also be produced by dark matter. If dark matter is composed of so-called weakly interacting massive particles (WIMPs), astrophysicists believe the WIMPs would sometimes annihilate one another and create an electron and a positron. These electrons and positrons might be visible as an excess number of particles, over and above what is expected from other sources.
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Since its launch in late 2015, the DAMPE satellite has logged more than 1.5 million CREs. As a general rule, particles with more energy are expected to be less common. The decrease in frequency of particles with increasing energy is expected to follow a smooth curve.
The new results, however, show a sharp change in the slope of the curve above an energy level of 0.9 teraelectronvolts (TeV). According to Fan Yinzhong, deputy chief designer of DAMPE’s experiments, this may indicate “the annihilation of [dark matter] particles with a mass of around 1–2 TeV”. He adds that there are also other potential explanations, such as nearby supernovae and pulsars. To confirm the presence of dark matter, he would want to see “a sharp edge” in the spectrum.
The DAMPE observations confirm and add detail to earlier CRE measurements, carried out from the ground and high-altitude balloons, that indicated the presence of the break in the spectrum.
