What Are Fast Radio Bursts, and What's Causing Them?

Background

A fast radio burst is an intense pulse of radio-frequency energy lasting only a few milliseconds, arriving with no warning and, in most cases, no repeat. Despite lasting less than the blink of an eye, a typical FRB releases roughly as much energy as the Sun radiates over several days, energy that has usually travelled from a galaxy millions or billions of light-years away, making the source among the most energetic single events astronomers observe.

Duncan Lorimer, an astronomer at West Virginia University, and his student David Narkevic found the first known example, later called the Lorimer Burst, in 2007 while re-examining pulsar survey data recorded by Australia's Parkes Observatory back on 24 July 2001. The finding was treated with caution for years afterward, not helped by the 2010 discovery that a separate class of signals detected at the same observatory, nicknamed "perytons," were eventually traced in 2015 to nearby microwave ovens being opened mid-cycle. Only once the burst's arrival-time signature, called its dispersion measure, was shown to match a signal that had crossed vast distances of intergalactic space did most astronomers accept the Lorimer Burst as a genuine extragalactic phenomenon rather than local interference or an instrumental artefact.

The Search for a Cause

For over a decade after 2007, FRBs were detected too rarely and too unpredictably for any single telescope to build a large catalogue. That changed when the Canadian Hydrogen Intensity Mapping Experiment (CHIME), a radio telescope in British Columbia built primarily to map the early universe's expansion, began operating in September 2018 and turned out to be extraordinarily effective at catching FRBs as an incidental byproduct of its main survey work. The catalogue grew from a few dozen confirmed events to several hundred within a few years, and now stands well over a thousand.

The most consequential single detection came on 28 April 2020, when CHIME and the independent STARE2 array both recorded an FRB-like burst arriving not from a distant galaxy but from within our own: specifically, from SGR 1935+2154, a magnetar, an extraordinarily magnetised type of neutron star, roughly 30,000 light-years away in the constellation Vulpecula. It was the first FRB-class event ever traced to a specific, directly observed source, and it confirmed that magnetars can, at least sometimes, produce genuine fast radio bursts through violent flares in their intense magnetic fields.

Why the Case Isn't Closed

The 2020 magnetar detection solved a narrower question than it is sometimes credited with solving: it showed magnetars produce at least one FRB, not that magnetars produce all of them. The population of catalogued bursts splits into two behaviourally distinct groups that any single explanation has to account for. The large majority appear to burst only once and are never heard from again, consistent with a violent, one-time event such as a magnetar flare or, in some proposed models, a neutron-star merger. A smaller but closely studied minority repeat from the same sky position, sometimes prolifically: FRB 121102, the first repeating source ever identified, produced 72 detected bursts in a single five-hour window in September 2018 alone. A few repeaters follow an apparent cycle altogether, most notably FRB 180916, whose bursts cluster into a roughly four-day active window followed by about twelve days of silence, a pattern that has itself resisted a fully settled explanation.

A small number of scientists, including Harvard astronomer Avi Loeb, whose past work on 'Oumuamua has made him a prominent voice on unconventional astrophysical explanations, have published speculative papers exploring whether some fast radio bursts, particularly the more energetic or precisely repeating ones, could in principle be produced by artificial technology rather than natural astrophysical processes. This idea has not been endorsed by any FRB's original discovery team and carries no direct observational support; mainstream astronomy treats it, at most, as a logically available but currently unevidenced possibility, in a field with a documented history of premature "artificial signal" speculation, including the "LGM-1" nickname briefly attached to the first pulsar discovery in 1967 before it was understood to be a natural, rapidly rotating neutron star.

Current Consensus

Astronomers agree magnetar flares are a confirmed, directly observed source of at least some fast radio bursts, and the leading working hypothesis for a large share of the wider population, both repeating and non-repeating. What remains genuinely open is whether every catalogued FRB shares this single mechanism or whether the population is a mixture of several different physical processes, including possible contributions from more catastrophic one-time events for at least some of the pure one-off bursts. With well over a thousand events now catalogued and CHIME-class instruments continuing to expand the sample rapidly, most researchers expect the remaining uncertainty to narrow through statistics and improved localisation rather than through any single decisive observation.

Why This Mystery Endures

Fast radio bursts endure as a live scientific frontier rather than a folklore-driven mystery, which sets them apart from most of this site's unexplained-signal coverage: the puzzle is not whether the phenomenon is real, it demonstrably is, and is detected on a near-daily basis, but which of several plausible physical mechanisms, or what mixture of them, actually produces the full range of observed behaviour. That structure, a real, richly documented dataset that keeps growing faster than theory can fully explain it, has made FRBs one of the most active corners of modern radio astronomy less than two decades after the first one was recognised in old survey data.

The comparison with the Wow! Signal is instructive precisely because the two cases sit at opposite ends of the same broad category, an unexplained flash of radio energy from space. The Wow! Signal was a single, never-repeated detection from 1977 that fifty years of searching has never managed to either explain or detect again, leaving it permanently underdetermined. Fast radio bursts are the reverse case entirely: thousands of confirmed detections, an actively growing catalogue, and at least one directly confirmed astrophysical source, yet still no single explanation that accounts for the whole population. Fast radio bursts are part of this site's space mysteries coverage.