Fast radio bursts (FRBs) are a rare and mysterious phenomenon. Until recently, we had seen fewer than 20 of these milliseconds-long pulses of radio waves, and they have been attributed to everything from quasars to aliens.

Last year, astronomers at the Arecibo Observatory in Puerto Rico nearly doubled the number of observed FRBs when they saw 16 bright bursts from the direction of FRB 121102, where a single burst had been detected in 2012.

Such repeating FRBs add another layer to the mystery. It’s possible that all FRBs repeat but our telescopes simply aren’t sensitive enough to detect most of them, or there could be more than one type of burst. Either way, we still don’t know what causes them.

Now, Zigao Dai at Nanjing University in China and his colleagues think they have a solution: pulsars playing bumper cars in a faraway asteroid belt.

If one of these fast-spinning stellar corpses got close enough to another planetary system to travel through its asteroid belt, it could rip electrons off the surface of any asteroids that got too close. The pulsar’s powerful electromagnetic field would accelerate those electrons to extraordinarily high energies, causing the radiation that we see as an FRB.

Such an encounter would be rare. But Dai and colleagues argue that the frequency of the bursts in FRB 121102 matches the distribution of asteroids in our solar system. Assuming other systems have a similar distribution, this adds to the theory’s plausibility, they say.

Extraterrestrial asteroids

Not everyone is convinced, though.

“It’s a little bit hand-wavy and fishy,” says Jason Hessels at the University of Amsterdam in the Netherlands who was on the team that discovered the repeating FRB signals. For one thing, we haven’t been watching FRB sources continuously, so we don’t actually know how often they repeat. “The bursts were separated by two weeks because we only observed once in two weeks – we don’t know what happened in between.”

We also don’t know what other asteroid systems look like. “If you wanted to, you could just add more asteroids in certain places to get whatever timescale you want or whatever duration of repetition you want,” he says. “It’s flexible to a fault.”

If the theory does turn out to be true, though, it could be a window into asteroids around other stars. “We could use the individual FRB pulses of different brightnesses and durations to learn about the size and shape of asteroids in a belt around a star in another galaxy,” says Emily Petroff at the Netherlands Institute for Radio Astronomy.

Source: New Scientist