If they’re that far away, then they must be very energetic. “At cosmological distances, this indicates that they are more luminous than bursts from any known transient radio source,” the authors noted, before concluding that this indicates “that the FRBs are likely cataclysmic in nature.” But it can’t be a rare cataclysm; based on the amount of sky surveyed and the frequency of the FRBs they detected, the authors estimated that as many as 104 might be visible across the entire sky.
So, what’s the cataclysm? That’s what’s hard to explain. The typical radio bursts we’ve seen are either repetitive (like a pulsar) or accompanied by signs at other wavelengths. These are neither. One option the astronomers considered was a neutron star merger, but those mergers are expected to be very rare and wouldn’t produce that much energy. The same problem faces an alternative explanation, which is that it could be the evaporation of a black hole—but it simply doesn’t produce enough energy. A supernova with an orbiting neutron star might produce this sort of energy, but those aren’t expected to be all that common.
So, for now, the source is a bit of a mystery. Which means astronomers will probably start devising ways to better pin down the locations of these events and do follow-ups with other hardware to try to see precisely where they originate and whether anything interesting is going on in the region. But, as an accompanying perspective notes, it took us decades to pin down the likely source of gamma-ray bursts, so it might not be wise to hope for a quick resolution to the mystery.
Science, 2013. DOI: 10.1126/science.1236789 (About DOIs).