Fast radio burst
In radio astronomy, a fast radio burst is a transient radio wave of length ranging from a fraction of a millisecond, for an ultra-fast radio burst, to 3 seconds, caused by a high-energy astrophysical process that is not yet understood. Astronomers estimate the average FRB releases as much energy in a millisecond as the Sun puts out in three days. 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. Many FRBs have since been recorded, including several that have been detected repeating in seemingly irregular ways. Only one FRB has been detected to repeat in a regular way: FRB 180916 seems to pulse every 16.35 days.
Most FRBs are extragalactic, but the first Milky Way FRB was detected by the CHIME radio telescope in April 2020. In June 2021, astronomers reported over 500 FRBs from outer space detected in one year.
When FRBs are polarized, it indicates that they are emitted from a source contained within an extremely powerful magnetic field. The exact origin and cause of FRBs is still the subject of investigation; proposals for their origin range from a rapidly rotating neutron star and a black hole, to extraterrestrial intelligence. In 2020, astronomers reported narrowing down a source of fast radio bursts, which may now plausibly include "compact-object mergers and magnetars arising from normal core collapse supernovae". A neutron star has been proposed as the origin of an unusual FRB with periodic peaks lasting over 3 seconds reported in 2022.
The discovery in 2012 of the first repeating source, FRB 121102, and its localization and characterization in 2017, has improved the understanding of the source class. FRB 121102 is identified with a galaxy at a distance of approximately three billion light-years and is embedded in an extreme environment. The first host galaxy identified for a non-repeating burst, FRB 180924, was identified in 2019 and is a much larger and more ordinary galaxy, nearly the size of the Milky Way. In August 2019, astronomers reported the detection of eight more repeating FRB signals. In January 2020, astronomers reported the precise location of a second repeating burst, FRB 180916. One FRB seems to have been in the same location as a known gamma-ray burst.
On 28 April 2020, a pair of millisecond-timescale bursts consistent with observed fast radio bursts, with a fluence of >1.5 million Jy ms, was detected from the same area of sky as the magnetar SGR 1935+2154. Although it was thousands of times less intrinsically bright than previously observed fast radio bursts, its comparative proximity rendered it the most powerful fast radio burst yet observed, reaching a peak flux of either a few thousand or several hundred thousand janskys, comparable to the brightness of the radio sources Cassiopeia A and Cygnus A at the same frequencies. This established magnetars as, at least, one ultimate source of fast radio bursts, although the exact cause remains unknown. Further studies support the notion that magnetars may be closely associated with FRBs. On 13 October 2021, astronomers reported the detection of hundreds of FRBs from a single system.
In 2024, an international team led by astrophysicists of INAF, using detections from VLA, NOEMA interferometer, and Gran Telescopio Canarias has conducted a research campaign about FRB20201124A, one of the two known persistent FRB, located about 1.3 billion light-years away. Based on the outcomes of the study, authors deem to confirm the origin of FRBs in a binary system at high accretion rate, that would blow a plasma bubble, responsible for the persistent radio emission. The emission object, i.e. the "bubble", would be immersed in a star-forming region.
Detection
The first fast radio burst to be described, the Lorimer Burst FRB 010724, was found in 2007 in archived data recorded by the Parkes Observatory on 24 July 2001. Since then, many FRBs have been found in previously recorded data. On 19 January 2015, astronomers at Australia's national science agency reported that a fast radio burst had been observed for the first time live, by the Parkes Observatory. Many FRBs have been detected in real time by the CHIME radio telescope since it became operational in 2018, including the first FRB detected from within the Milky Way in April 2020.In January 2025, astronomers discovered radio waves from a galaxy that is roughly 2-billion light years away from Earth and is believed to be more than 11 billion years old. These FRBs are associated with a galaxy that was believed to be dead.
Features
Fast radio bursts are bright, unresolved, broadband, millisecond flashes found in parts of the sky. Unlike many radio sources, the signal from a burst is detected in a short period of time with enough strength to stand out from the noise floor. The burst usually appears as a single spike of energy without any change in its strength over time. The bursts last for several milliseconds. The bursts come from all over the sky, and are not concentrated on the plane of the Milky Way. Known FRB locations are biased by the parts of the sky that the observatories can image.Many have radio frequencies detected around 1400 MHz; a few have been detected at lower frequencies in the range of 400–800 MHz. The component frequencies of each burst are delayed by different amounts of time depending on the wavelength. This delay is described by a value referred to as a dispersion measure. This results in a received signal that sweeps rapidly down in frequency, as longer wavelengths are delayed more.
Extragalactic origin
The interferometer UTMOST has put a lower limit of 10,000 kilometers for the distance to the FRBs it has detected, supporting the case for an astronomical, rather than terrestrial, origin. This limit can be determined from the fact that closer sources would have a curved wave front that could be detected by the multiple antennas of the interferometer.Fast radio bursts have pulse dispersion measurements, much larger than expected for a source inside the Milky Way galaxy and consistent with propagation through an ionized plasma. Furthermore, their distribution is isotropic ; consequently they are conjectured to be of extragalactic origin.
Origin hypotheses
Because of the isolated nature of the observed phenomenon, the nature of the source remains speculative., there is no generally accepted single explanation, although a magnetar has been identified as a possible source. The sources are thought to be a few hundred kilometers or less in size, as the bursts last for only a few milliseconds. Causation is limited by the speed of light, about 300 km per millisecond, so if the sources were larger than about 1000 km, a complex synchronization mechanism would be required for the bursts to be so short. If the bursts come from cosmological distances, their sources must be very energetic. Extending the technique of measuring pulsar emission region sizes using a scattering screen in the Milky Way, a method to estimate the transverse FRB emission region size using a scattering screen in the host galaxy was formulated in 2024. Within the same year, a previously recorded burst, FRB 202210122A, was constrained to have an emission region size less than 30,000 km, using this technique.One possible explanation would be a collision between very dense objects like merging black holes or neutron stars. It has been suggested that there is a connection to gamma-ray bursts. Some have speculated that these signals might be artificial in origin, that they may be signs of extraterrestrial intelligence, demonstrating veritable technosignatures. Analogously, when the first pulsar was discovered, it was thought that the fast, regular pulses could possibly originate from a distant civilization, and the source nicknamed "LGM-1". In 2007, just after the publication of the e-print with the first discovery, it was proposed that fast radio bursts could be related to hyperflares of magnetars. In 2015 three studies supported the magnetar hypothesis. The identification of first FRB from the Milky Way, which originated from the magnetar SGR 1935+2154, indicates that magnetars may be one source of FRB.
Especially energetic supernovae could be the source of these bursts. Blitzars were proposed in 2013 as an explanation.
In 2014 it was suggested that following dark matter-induced collapse of pulsars, the resulting expulsion of the pulsar magnetospheres could be the source of fast radio bursts. In 2015 it was suggested that FRBs are caused by explosive decays of axion miniclusters. Another exotic possible source are cosmic strings that produced these bursts as they interacted with the plasma that permeated the early Universe. In 2016 the collapse of the magnetospheres of Kerr–Newman black holes were proposed to explain the origin of the FRBs' "afterglow" and the weak gamma-ray transient 0.4 s after GW 150914. It has also been proposed that if fast radio bursts originate in black hole explosions, FRBs would be the first detection of quantum gravity effects. In early 2017, it was proposed that the strong magnetic field near a supermassive black hole could destabilize the current sheets within a pulsar's magnetosphere, releasing trapped energy to power the FRBs.
Plasma processes
A variety of plasma-based mechanisms have been proposed to explain the coherent radio emission observed in FRBs. These processes typically involve relativistic magnetized plasmas, such as those found near magnetars or in shocks, where collective plasma effects and radiative processes can lead to the generation of bright, short-duration radio pulses. One promising mechanism is coherent electromagnetic emission from relativistic magnetized shocks, where the shock propagates in an electron–positron plasma with high magnetization. These shocks generate X-mode polarized precursor waves through a synchrotron maser–like instability, with efficiencies and spectral features determined self-consistently via particle-in-cell simulations. The shocks can arise from magnetar flares driving relativistic outflows, and may convert a small fraction of their energy into coherent radio emission, consistent with observed FRB energetics. Another proposed mechanism is the electron cyclotron maser instability, which can be triggered when synchrotron cooling generates ring-shaped momentum distributions that are unstable to X-mode wave growth. This has been demonstrated in simulations of strongly magnetized plasmas where radiative losses sustain the coherent radio emission.Alternative models invoke coherent curvature radiation by bunched charges moving along curved magnetic field lines, often associated with magnetic reconnection near the surface or in the current sheet of neutron stars. In some versions, particle bunching is induced by plasma instabilities or perturbations in the magnetosphere. Other proposals include antenna-type mechanisms, where coherent structures in the plasma radiate collectively, and free electron laser -like processes driven by reconnection-generated particle beams in magnetized turbulence. In these models, particles interact with Alfvénic or electromagnetic wigglers and emit coherently via nonlinear Thomson or Compton-like scattering. Collectively, these plasma-based mechanisms aim to explain the high brightness temperatures, narrow-band spectra, and polarization features of FRBs, and are often framed within the magnetar scenario, although they may operate in broader astrophysical settings.