Fast Radio Bursts: Millisecond Cosmic Explosions From Across the Universe

More Energy Than the Sun Emits in Three Days, Released in a Millisecond

A fast radio burst (FRB) releases as much energy in a single millisecond as the Sun emits in approximately 3 days—yet the event is over before a human blink completes. These cosmic flashes of radio waves arrive from extragalactic distances, ranging from hundreds of millions to several billion light-years away, and each individual burst lasts between a fraction of a millisecond and a few tens of milliseconds. Since the first FRB was discovered in archival data in 2007, over 1,000 have been catalogued, and the CHIME telescope in Canada alone detects several per day. FRBs have transformed from a mysterious anomaly into one of astrophysics' most powerful cosmological tools.

The first known FRB—now called the Lorimer Burst after discoverer Duncan Lorimer—was found in 2007 by Lorimer and student David Narkevic while re-analyzing 2001 archival data from the Parkes radio telescope in Australia. The signal's dispersion measure (how the burst's lower frequencies arrived later than higher frequencies, due to electrons in intergalactic space) indicated it originated billions of light-years from Earth. Initial skepticism was significant—the signal was so brief and so distant that some astronomers suspected terrestrial radio frequency interference. Subsequent detections at multiple facilities confirmed FRBs as a genuine astrophysical phenomenon.

The Dispersion Measure: Nature's Distance Ruler

The most powerful tool for analyzing FRBs is the dispersion measure (DM)—a quantity that measures the column density of free electrons between the source and the detector. Radio waves at lower frequencies travel more slowly through ionized plasma than at higher frequencies. A burst traveling billions of light-years through the intergalactic medium arrives with its lower-frequency component measurably delayed relative to the higher-frequency component. This time delay, integrated over the path length, gives the DM.

Repeating vs. Non-Repeating FRBs

One of the most important distinctions in FRB research is between one-off bursts (detected once) and repeating sources (the same location emits multiple bursts over time). The first confirmed repeating FRB, FRB 121102A, was identified by the Arecibo Observatory in 2015 and has since emitted hundreds of detected bursts. Repeating FRBs are scientifically valuable because they allow precision localization—multiple burst detections with interferometric arrays can pin down the source position to a specific galaxy and even a specific region within that galaxy.

• Repeating FRBs cannot be explained by cataclysmic one-time events (black hole mergers, neutron star collisions)—the source must survive to emit again.
• FRB 121102A was localized to a dwarf galaxy at redshift z=0.19, approximately 3 billion light-years away—the first FRB associated with a specific host galaxy.
• The CHIME/FRB collaboration detected FRB 20180916B repeating on a 16.35-day periodicity, suggesting either orbital dynamics or rotation of the emitting object with a beam sweeping past Earth at regular intervals.
• Whether one-off and repeating FRBs share the same physical origin mechanism or represent distinct source classes remains an open question.

The Magnetar Connection

The 2020 detection of FRB 200428 revolutionized understanding of FRB origins. This burst was traced to SGR 1935+2154, a soft gamma repeater (a type of magnetar) located approximately 30,000 light-years away inside the Milky Way—the first FRB with a confirmed galactic source. The burst's properties closely matched extragalactic FRBs, scaled by distance. Magnetars—neutron stars with magnetic fields of 10¹³ to 10¹⁵ gauss, the strongest known in the universe—are now the leading candidate for the origin of at least some FRBs.

The proposed mechanism involves magnetic field reconnection or crustal "starquakes" in the magnetar surface, releasing enormous energy as coherent radio emission. However, the detailed radiation mechanism—how the energy converts specifically into bright, narrowband radio emission—remains under active theoretical investigation. And whether all FRBs originate from magnetars, or whether multiple source types produce similar-looking signals, has not been resolved.

FRBs as Cosmological Probes

Beyond their intrinsic interest as astrophysical events, FRBs have emerged as extraordinarily useful cosmological instruments.

• Mapping the intergalactic medium: The dispersion measure of each FRB constrains the electron column density along its line of sight, providing direct measurements of ionized gas in the space between galaxies—matter that had been extremely difficult to observe directly.
• Solving the "missing baryons" problem: Cosmological models predicted that roughly half of all normal (baryonic) matter in the universe should exist as warm-hot intergalactic gas—but decades of observations could account for only about half of this material. Statistical analysis of FRB dispersion measures across many lines of sight has provided evidence that this "missing" baryonic matter does exist as diffuse intergalactic plasma.
• Measuring the Hubble constant: Because FRB DM increases with distance, well-localized FRBs (where the host galaxy's redshift is known independently) can be used to independently estimate the Hubble constant—the expansion rate of the universe—contributing to ongoing debates about its precise value.

Telescope Infrastructure Driving FRB Science

The dramatic increase in FRB detection rates since 2018 is primarily attributable to the Canadian Hydrogen Intensity Mapping Experiment (CHIME), a fixed-overhead radio telescope in British Columbia that observes roughly half the sky each day. CHIME's wide field of view and high sensitivity allow it to detect FRBs at a rate that dwarfs all previous instruments combined. The CHIME/FRB project has published catalogs containing hundreds of new sources, enabling population statistics impossible with earlier datasets. Upcoming facilities including the Square Kilometre Array (SKA) in Australia and South Africa, expected to reach full operation in the late 2020s, will dramatically increase both detection rate and localization precision—likely transforming FRB science from a collection of notable individual events into a mature statistical discipline used routinely for cosmological measurement.