Fast radio bursts have been observed many times since they were first observed in 2007, but there is still not a good, widely accepted understanding of what causes them. Wikipedia, quoted below with citations omitted, explains what they are, and then, a new review article, that follows this quotation, sums up the current situation.
The prospects for finding answers to the FRB mystery, as in many lines of research for which astronomy data is relevant, is good, because we are in a golden age of astronomy in which immense waterfalls of data from multiple sources are gushing in and ready to provide answers once they are properly analyzed.
In radio astronomy, a fast radio burst (FRB) is a transient radio pulse of length ranging from a fraction of a millisecond to a few milliseconds, caused by some high-energy astrophysical process not yet identified. While extremely energetic at their source, the strength of the signal reaching Earth has been described as 1,000 times less than from a mobile phone on the Moon. The first FRB was discovered by Duncan Lorimer and his student David Narkevic in 2007 when they were looking through archival pulsar survey data, and it is therefore commonly referred to as the Lorimer Burst. Several FRBs have since been found, including two repeating FRBs. Although the exact origin and cause is uncertain, they are almost definitely extragalactic. When the FRBs are polarized, it indicates that they are emitted from a source contained within an extremely powerful magnetic field. The origin of the FRBs has yet to be identified; proposals for their origin range from a rapidly rotating neutron star and a black hole, to extraterrestrial intelligence.
The localization and characterization of the first detected repeating source, FRB 121102, has revolutionized the understanding of the source class. FRB 121102 is identified with a galaxy at a distance of approximately 3 billion light years, well outside the Milky Way, and embedded in an extreme environment.
Fast Radio Bursts: An Extragalactic Enigma
(Submitted on 13 Jun 2019)
We summarize our understanding of millisecond radio bursts from an extragalactic population of sources. FRBs occur at an extraordinary rate, thousands per day over the entire sky with radiation energy densities at the source about ten billion times larger than those from Galactic pulsars. We survey FRB phenomenology, source models and host galaxies, coherent radiation models, and the role of plasma propagation effects in burst detection. The FRB field is guaranteed to be exciting: new telescopes will expand the sample from the current∼80 unique burst sources (and a few secure localizations and redshifts) to thousands, with burst localizations that enable host-galaxy redshifts emerging directly from interferometric surveys.
* FRBs are now established as an extragalactic phenomenon.
* Only a few sources are known to repeat. Despite the failure to redetect other FRBs, they are not inconsistent with all being repeaters.
* FRB sources may be new, exotic kinds of objects or known types in extreme circumstances. Many inventive models exist, ranging from alien spacecraft to cosmic strings but those concerning compact objects and supermassive black holes have gained the most attention. A rapidly rotating magnetar is a promising explanation for FRB 121102 along with the persistent source associated with it, but alternative source models are not ruled out for it or other FRBs.
* FRBs are powerful tracers of circumsource environments, `missing baryons' in the IGM, and dark matter.
* The relative contributions of host galaxies and the IGM to propagation effects have yet to be disentangled, so dispersion measure distances have large uncertainties.
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