“A minor point of interest regarding the Spitler Burst.” The email subject line popped up on Shami Chatterjee’s computer screen just after 3 in the afternoon on Nov. 5, 2015.
When Chatterjee read the email, he first gasped in shock — and then sprinted out of his Cornell University office and down the corridor to tell a colleague. Twenty-eight minutes later, when he started to draft a reply, his inbox was already buzzing. The email thread grew and grew, with 56 messages from colleagues by midnight.
For nearly a decade, Chatterjee and other astrophysicists on the thread had been trying to understand the nature of short, superenergetic flashes of radio waves in space. These “fast radio bursts,” or FRBs, last just a few milliseconds, but they are the most luminous radio signals in the universe, powered by as much energy as 500 million suns. The first one was spotted in 2007 by the astronomer Duncan Lorimer, who together with one of his students stumbled upon the signal accidentally in old telescope data; at the time, few believed it. Skeptics suspected interference from mobile phones or microwave ovens. But more and more FRBs kept showing up — 26 have been counted so far, including the Spitler burst, detected by the astronomer Laura Spitler in data from 2012 — and scientists had to agree they were real.
The question was, what causes them? Researchers sketched dozens of models, employing the gamut of astrophysical mysteries — from flare stars in our own galaxy to exploding stars, mergers of charged black holes, white holes, evaporating black holes, oscillating primordial cosmic strings, and even aliens sailing through the cosmos using extragalactic light sails. For scientists, the FRBs were as blinding as flash grenades in a dark forest; their power, brevity and unpredictability simply made it impossible to see the source of the light.