Fast Radio Bursts (FRBs) are very quick and very large emissions of radio waves. Their sources are unclear, and there is a lot we don’t know about them. FRB 20180916B is among the few that repeat with a well-defined period. A compelling explanation was put forward to explain this mysterious object – but it appears that it’s wrong.
FRB 20180916 repeats every 16.3 days, with the bursts being emitted within a 5-day window followed by radio silence for the following days. Suggested at first, one hypothesis was that the source orbits a companion, only producing FRBs at certain points through its orbit.
This idea explained a lot of the weirdness, but it began cracking earlier this year. Astronomers discovered that different wavelengths of radio waves were emitted at different points, something not consistent with that binary star model. The findings are available on ArXiV and are yet to be peer-reviewed.
The team compares the observations to what we might see in visible light. Short radio wavelengths, akin to blue light in the team’s analogy, appeared for the first two days of the burst. This is expected from FRB models coming from a pair of orbiting stars. However, observations showed that longer radio emission, akin to red light, showed up for the following three days. This shouldn’t be the case.
“Strong stellar winds from the companion of the Fast Radio Burst source were expected to let most blue, short-wavelength radio light escape the system. But the redder long-wavelength radio should be blocked more, or even completely,” lead author, Inés Pastor-Marazuela from the University of Amsterdam and ASTRON said in a statement.
The observations throw a spanner in the works of the binary star model, but are not enough to explain what is actually causing the FRBs from this object. The main explanation remains that the source is a magnetar, a type of neutron star with an incredible magnetic field. Neutron stars form when stars in a certain mass range go supernova. Shrinking down the mass of our Sun into something not much bigger than a tropical island creates objects that spin on their axis incredibly quickly – some hundreds of times per second.
Here lays the problem for this model. A singular magnetar can explain these observations, but only if it rotates on its axis very slowly – about 100,000 times more slowly than any other known neutron star period.
The origin of FRB 20180916 continues to elude humanity, but these observations have shown that FRBs emit signals to longer wavelengths than previously thought. There’s more to study about them. FRB 20180916 comes from a galaxy 500 million light-years away.