In 2007, astrophysicist Duncan Lorimer was sifting through six-year-old archived data from an Australian radio telescope when he found something buried in the noise: a signal lasting roughly five milliseconds, so bright and so distorted by its journey that it appeared to have traveled billions of light-years to reach Earth. Whatever produced it released more energy in a few thousandths of a second than the Sun radiates over days. Nearly two decades later, astronomers have detected thousands of similar bursts and finally traced one directly to its source, and yet what's actually producing most of them remains one of the most actively contested open questions in modern astrophysics.
Background: A Signal Hidden in Old Data
What Lorimer found, retrospectively analyzing archival data from the Parkes radio telescope in Australia, became known as fast radio bursts, or FRBs: extraordinarily bright, millisecond-duration pulses of radio energy arriving from deep space. Astronomers can estimate roughly how far a burst traveled using a property called its dispersion measure, essentially a record of how much the signal's different frequencies were delayed and spread out as they passed through ionized gas on their way to Earth. The more dispersed a signal is, the more intervening material it likely traveled through, and the original Lorimer Burst showed dispersion consistent with an origin far outside our own galaxy, implying a source of genuinely extreme power.
The Repeat Offender and the 2020 Breakthrough
For roughly the first decade after their discovery, only a handful of FRBs were ever detected, and nearly all of them appeared to be one-time events, single pulses that never repeated. That changed with FRB 121102, first detected in 2012 and confirmed as the first known repeating FRB, a source that produced multiple bursts over time rather than a single flash. In January 2017, researchers traced FRB 121102 to a small dwarf galaxy and proposed its source was likely a magnetar, a type of neutron star with an extraordinarily powerful magnetic field.
The most significant confirmation came in April 2020, when astronomers detected FRB 200428, a burst that, unlike nearly every FRB found before it, originated from within our own Milky Way galaxy. Its source was identified as SGR 1935+2154, a known magnetar previously studied only for its bursts of soft gamma-ray emission. Crucially, the radio burst coincided almost exactly with a series of X-ray bursts from the same object, detected simultaneously by two independent instruments, the Canadian CHIME telescope and the STARE2 detector array. It was the first direct observational link connecting a magnetar to an FRB-like event, giving researchers their strongest evidence yet for what at least some fast radio bursts actually are.
An Explosion of Detections
The pace of discovery has accelerated dramatically since the Canadian Hydrogen Intensity Mapping Experiment, or CHIME, began systematically surveying the sky. What had been a population of roughly 60 known FRBs as recently as 2018 grew to hundreds within a few years and now numbers in the thousands, with researchers estimating the true rate across the entire sky is likely far higher still, limited mainly by how much sky any single telescope can observe at once.
Cosmic Anomalies at a Glance
| Anomaly | What's Observed | Leading Explanation | Status |
|---|---|---|---|
| Fast Radio Bursts | Millisecond-long, extremely energetic radio pulses from deep space | Magnetar activity, confirmed for at least one source | Active research; likely multiple distinct causes |
| Planet Nine | Unusual clustering in the orbits of distant icy solar system objects | An undiscovered large planet in the outer solar system | Unconfirmed; active search ongoing |
| The Great Attractor | Thousands of galaxies, including our own, drawn toward one region | A massive, largely hidden concentration of galaxy clusters | Partially mapped; obscured by the Milky Way's disk |
| CMB Cold Spot | An unusually cold, large region in the cosmic microwave background | Statistical fluke, or a massive cosmic void | Debated; no fully settled explanation |
| Axis of Evil (CMB Anomaly) | Unexpected large-scale alignment in cosmic background radiation patterns | Possible instrument or foreground contamination | Unresolved; challenges assumptions about cosmic randomness |
Theories and Explanations
Magnetar giant flares. The 2020 detection of FRB 200428 from a known Galactic magnetar gave this theory its strongest observational support to date, though researchers are careful to note that this single confirmed case doesn't necessarily explain every FRB, particularly the more extreme, highly active repeating sources that don't fit the same pattern as neatly.
Neutron star or black hole mergers. For FRBs that appear to be genuine one-off events, some researchers propose cataclysmic mergers between extremely dense objects, such as two neutron stars, as an alternative source capable of releasing a comparably enormous burst of energy in an instant.
More exotic physics. A minority of theoretical proposals have explored more speculative mechanisms, including interactions involving hypothetical objects like cosmic strings, though these remain far more speculative than the magnetar-based explanations currently favored by most working astrophysicists.
Multiple distinct causes. Given how differently repeating and one-off FRBs behave, a growing number of researchers suspect that "fast radio burst" may turn out to be a broad observational category covering more than one genuinely different underlying phenomenon, rather than a single mystery with one final answer.
The Curious Connection
Fast radio bursts open this new series by illustrating something the earlier Space Mysteries series, and its coverage of the 1977 Wow! Signal, couldn't fully demonstrate: what happens when an unexplained cosmic signal stops being a single, unrepeatable data point and instead becomes a large, growing, statistically analyzable dataset. The Wow! Signal has remained genuinely unresolved for nearly fifty years precisely because it was never detected again. FRBs share a superficially similar mystery, an intense, brief burst of radio energy from deep space, but astronomers now have thousands of examples to compare, cross-reference, and test theories against, which is exactly the kind of accumulating evidence that eventually let researchers confirm at least one FRB's magnetar origin in 2020.
That distinction, mysteries that resist explanation for lack of data versus mysteries actively being narrowed down through accumulating observation, is the theme this new series will trace across each of its entries, from a hypothesized planet at the edge of the solar system to unexplained patterns baked into the oldest light in the universe.
Frequently Asked Questions
What is a fast radio burst?
A fast radio burst, or FRB, is an extremely bright, millisecond-duration pulse of radio energy originating from deep space, first discovered in 2007 by astrophysicist Duncan Lorimer while analyzing archival radio telescope data.
What causes fast radio bursts?
The leading explanation, strongly supported by a 2020 detection linking a burst to a known magnetar within the Milky Way, involves powerful magnetic activity from magnetars, a type of neutron star. Not all FRBs may share this same cause.
Are fast radio bursts dangerous to Earth?
No. FRBs originate from sources typically thousands to billions of light-years away, and by the time their energy reaches Earth, it poses no threat.
How many fast radio bursts have been detected?
Detections have grown from roughly 60 known sources as of 2018 to thousands today, driven largely by the Canadian CHIME telescope's systematic sky surveys.
Do all fast radio bursts repeat?
No. Most detected FRBs appear to be one-time events. A smaller subset, including the first confirmed repeating source, FRB 121102, produce multiple bursts over time, a distinction that may point to more than one underlying cause.