Discovered in 2007, fast radio bursts (FRBs) emit luminous pulses of radio light that last mere milliseconds. To date, astronomers have reported about 20 FRBs but don’t know what causes them. One, identified in 2014 by Laura Spitler and colleagues, stands apart because it has been observed to burst repeatedly (see Physics Today, April 2016, page 22). The source was first detected on 2 November 2012, hence its designation FRB121102. An international team took advantage of FRB121102’s ongoing intermittent activity to run a series of follow-up observations with several radio telescopes in the US and Europe and has located FRB121102 with unprecedented precision. The radio observations didn’t just refine the location of FRB121102, they also spotted a persistent source coincident with the FRB, to within experimental uncertainty. It is possible that the persistent source is related to the FRB; it could be, for example, a highly energetic neutron...

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