Gravitational waves reveal part of the secret of fast radio bursts

on the informative site ConversationClancy astrophysicist William James recently discussed a discovery made by his colleagues and published in an article in the popular journal natural astronomy. A copy of the publication is freely available at arXiv. It demonstrates once again the fact that with the discovery of gravitational waves on Earth, we have fully entered the era of multimessage astronomy. From now on, we can already correlate signals in the form of electromagnetic waves with signals in the form of undulating warping of the fabric of space-time to analyze still somewhat mysterious astrophysical phenomena.

In this case, these are fast radio bursts (fast radio blasts, or FRB in English), also called “Lorimer bursts”, after its discoverer. As Futura has shown many times, FRBs are transient signals where the equivalent of all the energy radiated by the Sun in the visible for a year seems to have been released in milliseconds at most in the radio domain. When they were discovered through new analyzes of archival data collected by the Parkes radio telescope in Australia, it wasn’t yet clear if they were anything new or just false signals. This hypothesis was eventually refuted, and the first reliable estimates of the distances from the sources of the FRBs had them as extragalactic phenomena, implying that the energy released in such a short time must be so enormous that it could be detected from far away.

Since 2018, with the opening of a new major radio telescope at the Dominion Radio Astrophysical Observatory, in British Columbia, Canada, we’ve had a powerful tool for studying FRBs in the radio field. It was called the Canadian Hydrogen Intensity Mapping Experiment, or, in English, Canadian hydrogen intensity mapping experimentThus, in short, chemistry.

Video presentation of the Resonance Radio Telescope. For a more or less accurate French translation, click on the white rectangle at the bottom right. Then the English translation appears. Then click on the cogwheel to the right of the rectangle, then click on Subtitles and finally on Translate automatically. Choose “French”. © McGill University

FRBs, magnetism or black holes in formation?

As Clancy James explains, one of the theories explaining the potential nature of FRBs was supported by the detection on April 28, 2020 of a fast radio burst clearly associated with the celestial vault with Magnetar SGR 1935+2154, a neutron star with a particularly intense magnetic field.

Another theory for FRBs involves the collision of neutron stars. They then merge to temporarily give rise to a larger neutron star, which collapses very quickly into a black hole. But it turns out that, as the Nobel Prize in Physics Vitaly Ginzburg showed more than 50 years ago, a black hole cannot possess a magnetic field by generating neutrons from a star, even a star. Processes related to electromagnetic field theory must occur in curved space-time, which will lead to the formation black hole not inheriting the magnetic field of the protostar (this is an illustration of the famous balding black hole theory). However, the changing magnetic field generates a changing electric field and in fact quite electromagnetic waves.

So one could also think that some FRBs in fact betrayed the process theoretically predicted by Ginzburg. But since colliding neutron stars are also known to produce gravitational waves, it is predictable that the FRB could be detected in association with the source of the gravitational waves.

This is what happened with colleagues astrophysicist Alexandra Moroyano of the University of Western Australia. FRB 20190425A, detected in 2019 with Chime, occurred about two and a half hours after Ligo detected the gravitational wave source GW190425, a source whose signal structure made it possible to conclude that it came from the collision of two neutron stars.

It is difficult to imagine that the association is a coincidence because the estimated distances of the two sources are the same and thus they did indeed occur at very close dates. However, we do know how to estimate the rate of the neutron star collisions that give rise to FRBs and it does not appear to be large enough to explain the majority of detected FRBs. So the paradigm with magnetism is always complementary to that with neutron star mergers, as always shown Clancy W James.

The researcher concludes that it is still necessary to discover many events of this kind in order to remove all doubts regarding this connection between gravitational waves and the FRB. But as the sensitivity of detectors continues to increase, this should happen in the near future.