It started with a bang – at least, it must have. Astronomers have spotted a weird radio signal from space that appears to be the shock wave from an enormous explosion, but we never saw the explosion itself.
Casey Law at the University of California Berkeley and his colleagues were comparing two maps of radio wave sources in the sky when they noticed something strange: an object that had been one of the brightest on a map generated in 1993 had faded by a factor of 50 on a second map made in 2017.
That’s an unusually fast decline in brightness, so they examined archival data from several other telescopes to try to figure out what the object – called FIRST J141918.9+394036 or simply J1419 – really is.
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They found that it was likely the afterglow of a huge star collapsing in on itself to become either a dense neutron star or a black hole. When this happens, it can release incredibly powerful jets of radiation called gamma ray bursts (GRBs). Until now, we could only detect a GRB if a jet was pointing directly at Earth.
J1419 is the first time we’ve spotted a GRB that was pointing away from us. “As the jets are blasting out from the star, they’re putting a lot of energy into the outer layers of the star, and that energy has to come out in some form,” says Law. That radiated extra energy is likely what the researchers saw rapidly fading away since 1993.
“We heard the thunder, but didn’t see the lightning,” says Law. “If it was a gamma ray burst that was pointed at us, it would have been one of the brightest ever known.”
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