Astronomers Still Can’t Explain Fast Radio Bursts

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

As with most things in the universe, FRBs existed before humans and will probably continue happening long after we are gone. However, we only noticed them in 2012 when researchers reviewed radio telescope data from 2006. Since then, dozens of FRB sources have been spotted. Their extremely short duration and unpredictability made it difficult to come to any conclusions, but the more recent discovery of repeating FRBs was a watershed moment. Using one of these repeating sources, researchers from the University of Amsterdam and ASTRON in the Netherlands tested the leading FRB explanation.

With repeating bursts, like FRB 20180916B that was the focus of the new Dutch study, it’s possible to gather much more data on each event. FRB 20180916B flashes once every 16.35 Earth days, so the team felt it would be a perfect test for the leading binary-wind model. According to the hypothesis, FRBs are the result of interactions between two orbiting objects like a neutron star and a black hole.

Unfortunately, the data from FRB 20180916B doesn’t support the binary system hypothesis. If the 16-day periodicity of this signal was the result of orbiting partners, the longer red wavelengths should be diminished or even blocked completely. That would leave only short blue-shifted wavelengths. However, the researchers found no such correlation. On some days, the signal was red-shifted, and on others, it was more toward the blue end of the spectrum.

There has also been a lot of interest in magnetars as a potential source of FRBs. These neutron stars encased in powerful magnetic fields appear to be associated with at least some FRBs, but this isn’t an entirely satisfactory explanation either. These objects have wobbling rotations that could produce repeating effects like an FRB, but none of them wobble slowly enough to match known repeating signals. Even if the binary-wind model doesn’t pan out, we know so much more than we did just a few years ago. It feels like we’re zeroing in on the mechanism, whatever it turns out to be.

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