Astronomers still can’t explain rapid radio bursts

Few astronomical phenomena have been as upsetting in recent years as rapid radio bursts. These momentary flashes release as much energy in a millisecond as the sun does in three days, and the mechanism behind them remains a mystery. Astronomers have learned a lot about FRBs, but one of the main explanations has failed a critical test. It’s not quite back to the drawing board, but the remaining possibilities don’t quite fit the data either.

As with most things in the universe, FRBs existed before humans and will likely continue to occur long after we are gone. However, we didn’t notice them until 2012, when researchers looked at data from the 2006 radio telescope. Since then, dozens of FRB sources have been spotted. Their extremely short duration and unpredictability made it difficult to draw conclusions, but the more recent discovery of repeat FRBs was a turning point. Using one of these repeated sources, researchers at the University of Amsterdam and ASTRON in the Netherlands tested the main FRB explanation.

With repetitive bursts, like FRB 20180916B which was the focus of the new Dutch study, it is possible to collect much more data on each event. FRB 20180916B flashes once every 16.35 Earth days, so the team felt this would be a perfect test for the main binary wind model. According to the hypothesis, FRBs are the result of interactions between two orbiting objects such as a neutron star and a black hole.

The LOFAR telescope was essential for testing the binary wind model.

Unfortunately, the data from FRB 20180916B does not support the binary system hypothesis. If the 16-day periodicity of this signal was the result of partners in orbit, the longer red wavelengths would have to be decreased or even completely blocked. This would only leave short wavelengths shifted towards the blue. However, the researchers found no such correlation. Some days the signal was shifted red, and on others it was more towards the blue end of the spectrum.

Magnetars have also generated a lot of interest as a potential source of FRB. These neutron stars locked in strong magnetic fields appear to be associated with at least a few FRBs, but this is also not a fully satisfactory explanation. These objects have oscillating rotations that could produce repeated effects like an FRB, but none of them oscillate slowly enough to match known repeated signals. Even though the binary wind model doesn’t work, we know so much more than just a few years ago. It is as if we are focusing on the mechanism, whatever it is.

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