Are quick radio bursts brought on by the impression of interstellar objects on neutron stars?

Every now and then astronomers discover a strange radio signal. So powerful that it can outshine a galaxy, but only lasts milliseconds. They are called Fast Radio Bursts (FRBs). When they were first discovered a few decades ago, we had no idea what might be causing them. We weren't even sure if they were astronomical in origin. FRBs were so localized and so short-lived that it was difficult to collect data about them. But with wide-field radio telescopes like CHIME, we can now regularly observe FRBs and have a pretty good idea of ​​their source: magnetars.

Magnetars are neutron stars with immensely strong magnetic fields. Now that we can locate FRBs, we have been able to assign some of them to the region of a neutron star. While most FRBs occur in distant galaxies, we observed one in the Milky Way in 2020. The magnetar source also happened to be a pulsar, and astronomers were able to show that the FRB [correlated with a glitch in the pulsar’s rotation,](https://briankoberlein.com/blog/power-of-magnetism/) and thus confirms the source. Therefore, we are fairly certain that FRBs are caused by neutron stars, but we are still unsure about the exact mechanism.

One popular idea is that fast radio bursts are caused by magnetic realignments. This is what powers flares on the sun. Over time, the sun's magnetic field lines can twist until they realign, releasing energy in the process. If a similar effect occurs with magnetars, the resulting snapshot would be much faster and stronger. One difficulty with this idea is that FRBs are so short-lived that they are almost too fast for magnetic field lines to realign. So astronomers continue to look for new ideas, and one recently proposed argues that they are caused by impact events.

Distribution of FRB duration and ISB sizes in comparison. Photo credit: Pham et al

Collisions have long been known as a source of high-energy events. For example, some supernovae are caused by collisions of neutron stars. We also know that comets and asteroids occasionally impact the Sun, so we would expect similar impacts to occur with neutron stars. In this new work, the authors propose that FRBs are formed when an interstellar body collides with a neutron star. The impact would trigger a powerful electromagnetic burst. To support their argument, the authors examined the distribution of FRBs by duration. The timing of FRBs follows a distribution similar to the distribution of bodies in the solar system. Furthermore, the duration of an FRB appears to correspond to the hypothetical duration of an impact event based on an object's size.

While the data appears to support the idea of ​​impact-based FRBs, the study does not solve all of the mysteries surrounding these powerful eruptions. For example, we know that some FRBs are repeaters, meaning that they originate multiple times from the same source. Some studies have shown that repeating FRBs are quasi-periodic, which would be difficult to explain by random collisions. It is possible that repetitive and non-repetitive FRBs are caused by different mechanisms, although the data are not yet clear on this point.

Reference: Pham, Dang et al. “Fast radio bursts and interstellar objects.” arXiv preprint arXiv:2411.09135 (2024).

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