Something shadowy has reached out across the void from deep within the swirling Perseus galaxy cluster. X-ray observations of the cluster, shown here in false colour, have revealed a signal from an unidentified source.
Astronomers using the European Space Agency's XMM-Newton space telescope and NASA's Chandra telescope found similar signals in more than 70 galaxy clusters. It is possible that these X-rays are being produced by the decay of mysterious sterile neutrinos, as yet undiscovered particles that are predicted to barely interact with ordinary matter.
This lack of interaction makes sterile neutrinos a prime candidate to explain dark matter, the invisible stuff thought to make up most of the matter in the universe. The X-rays have an energy of around 3.5 kiloelectronvolts (keV), which could be produced by the decay of sterile neutrinos that weigh in at 7 keV, close to the mass predicted by dark matter models.
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