Fast Radio Bursts Explained: The Millisecond Flashes Brighter Than a Galaxy — and Nobody Knows What's Making Them

Something just flashed across the universe. It lasted one millisecond. In that millisecond, it released roughly the same energy our Sun will radiate over an entire day. And we still don't fully understand what made it.

These are fast radio bursts — the most energetic, least understood signals in modern astronomy. They come from billions of light-years away. Most happen exactly once. Scientists have been detecting them for under 20 years and are still arguing about the cause.

What is a fast radio burst?

A fast radio burst is a sudden, violent flash of radio waves arriving from deep space. Not visible light — radio waves. The same broad type of electromagnetic radiation as your Wi-Fi signal, but incomparably more powerful, and arriving from somewhere billions of light-years away.

The burst lasts less than a millisecond. Shorter than your reaction time. Briefer than a single frame of video. In that fraction of a second, a typical bright FRB radiates roughly as much energy as our Sun produces in an entire day. All of it. Compressed into an instant.

As the burst travels through intergalactic space, it passes through thin clouds of electrons drifting between galaxies. Those electrons smear the signal slightly — shorter wavelengths arrive a fraction of a second before longer ones. This delay, called dispersion, acts as a fingerprint. Measure it precisely and you can calculate how far the signal traveled, and through what kind of cosmic environment it passed.

Who discovered fast radio bursts?

The first one was hiding in old data.

In 2007, astrophysicist Duncan Lorimer was reviewing archival telescope recordings from 2001 when he found something that made no sense. A flash of radio waves — blindingly bright, lasting a fraction of a second — arriving from somewhere outside the Milky Way entirely. This became known as the Lorimer Burst: the first confirmed fast radio burst in history.

Nobody believed it. The signal was so strange, so brief, so energetic that most scientists assumed interference. A microwave oven near the telescope. A satellite reflection. A broken sensor. Skeptics coined the term "perytons" for human-made interference events that mimicked cosmic signals.

Then more telescopes started finding them. The CHIME telescope in British Columbia — a strange instrument that looks like a series of ski-slope half-pipes covered in antenna mesh — became the world's most prolific FRB detector, logging hundreds of confirmed bursts per year.

That last number. Scientists estimate roughly 800 fast radio bursts bright enough to detect could be striking Earth's full sky every single day. We catch a tiny fraction. The universe is sending signals we haven't built enough instruments to read yet.

Where do fast radio bursts come from?

For over a decade: nobody knew. The bursts were too brief to trace precisely. They came from every direction equally. No pattern. No source. No explanation.

Then, on April 28, 2020, a magnetar in our own Milky Way solved most of the mystery in a single afternoon.

A magnetar designated SGR 1935+2154 — a neutron star barely 20 kilometres across, located about 30,000 light-years from Earth — produced a burst of radio waves. Scientists analyzed it. It looked exactly like a fast radio burst.

Magnetars are the most extreme objects we know of. When a massive star explodes as a supernova, its core can collapse into a magnetar: a city-sized ball of nuclear matter with a magnetic field a quadrillion times stronger than Earth's. When the magnetar's crust cracks — a starquake — it unleashes a violent outburst of energy. For a sufficiently powerful quake, that energy becomes a fast radio burst. Bright enough to be seen from billions of light-years away.

CHIME, NASA, and multiple international teams simultaneously confirmed the connection. The magnetar hypothesis is now the scientific consensus. However, scientists are careful to note it doesn't cleanly explain everything. Some FRBs are more energetic than magnetar models comfortably predict. The repeating ones are particularly puzzling. Magnetars are the best current answer — not a closed case.

Do fast radio bursts repeat?

Most don't. Most fire once — from billions of light-years away — and are never heard from again.

But some do repeat. And those are even stranger than the one-off events.

FRB 20180916B, detected by CHIME in 2020, repeats on an almost clockwork 16-day cycle. It bursts actively for roughly four days. Then goes completely silent for twelve. Then returns. Like a metronome operating on cosmic timescales.

Random magnetar starquakes shouldn't produce that kind of regularity. Something more structured is happening. Current proposals include orbital geometry — a companion star periodically shadowing or amplifying the signal — or a neutron star precessing through a surrounding cloud of material on a predictable schedule. None of these are confirmed. It remains an open question.

Can fast radio bursts solve the universe's missing matter problem?

This is where FRBs stop being just a mystery and start being a tool.

Cosmological models have predicted for decades that roughly half of all ordinary matter in the universe — atoms, protons, electrons — should exist in incredibly thin, invisible wisps of gas drifting between galaxies. Not dark matter. Normal matter. Just spread too diffuse to detect with any conventional instrument. For 30 years, observers couldn't find it. It became known as the "missing baryon problem."

Fast radio bursts pass through that diffuse intergalactic gas. Each electron interaction delays the signal by a measurable amount. In 2020, astronomer Jean-Pierre Macquart and colleagues used five precisely localised FRBs to directly measure the density of that invisible matter — and confirmed the missing baryons were there all along, hiding in the spaces between galaxies.

This relationship is now called the Macquart relation. Every new FRB with a known source galaxy adds another measurement of the cosmic web's structure. What began as an interference signal nobody believed in has quietly become one of the most powerful cosmological instruments in modern astronomy.

Could fast radio bursts be artificial signals?

It's the question everyone in the room is thinking. Few astronomers say it out loud.

Harvard astrophysicist Avi Loeb — also known for arguing that Oumuamua might be artificial — co-authored a peer-reviewed 2017 paper proposing that FRBs could theoretically be the beam exhaust of a civilisation powering a lightsail. The physics actually works: you'd need something like a 2-kilometre transmitter array. The paper was published in the Astrophysical Journal Letters. It was not dismissed. It was discussed at conferences.

Most astronomers remain unconvinced. Magnetars are natural, well-evidenced, and don't require invoking civilisations. Known repeaters show no message structure. They arrive from all directions with no preferential sources that stand out as technological.

But here's what responsible scientists actually say: SETI programs actively include FRB data in their search programs. Not because researchers believe FRBs are artificial — but because scientific honesty requires ruling things out with data, not assumption. That's not a conspiracy. That's the standard.

We've catalogued over a thousand signals from outside our galaxy in under 20 years. Some repeat on regular timescales. We've traced them to specific galaxies billions of light-years away. We've used them to map matter invisible to every other telescope. And we still don't have a complete explanation for any individual burst.

That's not a mystery story. That's a description of where science actually stands right now.

If unexplained signals — from cosmic radio waves to declassified military footage — are your territory, the PURSUE UAP archive on SkyLens covers 375 government-released cases with the same evidence-first standard. The live tracker shows every catalogued object currently orbiting Earth in real time. And for more stories at the edge of what we actually know, the SkyLens blog has you covered.