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Since 2007, astronomers discovered and catalogued about 20 brief, superbright flashes of radio waves, which the called "Fast Radio Bursts" (FRBs).
The First FRB (FRB 010724) was discovered in 2007 in archived data taken in 2001 by the Parkes radiotelescope in Australia. Analysis of the data found a 30-jansky dispersed burst which occurred on 24 July 2001, less than 5 milliseconds in duration, located 3° from the Small Magellanic Cloud. The reported burst properties argue against an origin in the Milky Way galaxy or the Small Magellanic Cloud. The burst became known as the "Lorimer Burst." The discoverers argue that current models for the free electron content in the universe imply that the burst is less than 1 gigaparsec distant. The fact that no further bursts were seen in 90 hours of additional observations implies that it was a singular event.
In 2010, there was a report of 16 similar pulses detected by the Parkes radio telescope: but these were of terrestrial origin: they came from an open microwave oven doors suddenly opened during a heating cycle!
In 2013, four bursts were identified that supported the likelihood of extragalactic sources. FRB 140514, caught 'live' in 2014, was found to be 21% (+/- 7%) circularly polarised. Fast radio bursts discovered up until 2015 had dispersion measures that were close to multiples of 187.5 cm-3 pc. But subsequent observations dis not fit this pattern.
In 2015, FRB 110523 was discovered in archival data from the Green Bank Telescope. It was the first FRB for which linear polarization was detected (allowing, with the detection of circular polarisation, a calculation of Faraday rotation). Measurement of the signal's dispersion delay suggested that this burst is of extragalactic origin, possibly up to 6 billion light years away.
After investigation, most scientists estimated that these FRBs seem to be coming from galaxies billions of light-years away from ours.
FRBs have pulse dispersion measures which are much larger than expected for a source inside the Milky Way and consistent with propagation through an ionized plasma,[2] and furthermore their distribution is isotropic (not especially coming from the galactic plane), thus they are conjectured to be of extragalactic origin.
On 18 April 2015, FRB 150418 was detected by the Parkes observatory and within hours, several telescopes including the Australia Telescope Compact Array caught an "afterglow" of the flash, which took six days to fade. The Subaru telescope was used to find what was thought to be the host galaxy and determine its redshift and the implied distance to the burst. But the origin of the burst was soon disputed, and by April 2016 it was established that the emission instead originates from an active galactic nucleus that is powered by a supermassive black hole with dual jets blasting outward from the black hole. It was also noted that what was thought to be an "afterglow" never faded away, meaning that it cannot be associated with the fast radio burst.
In November 2015, astronomer Paul Scholz at McGill University in Canada found ten non-periodically repeated fast radio pulses in archival data gathered in May and June 2015 by the Arecibo radio telescope. The ten bursts have dispersion measures and sky positions consistent with the original burst FRB 121102, detected in 2012. Like the 2012 burst, the 10 bursts have three times the maximum plasma dispersion measure from a source in the Milky Way Galaxy. The team thinks that this finding rules out self-destructive, cataclysmic events that could only occur once, such as the explosion of a black hole or the collision between two neutron stars. According to the scientists, the data support an origin in a young rotating neutron star (pulsar), or in a highly magnetized neutron star (magnetar), or from highly magnetized pulsars travelling through asteroid belts, or from an intermittent Roche-lobe overflow in a neutron star-white dwarf binary.
On December 16, 2016, 6 new FRBs were reported in the same direction. This is the only known instance in which these signals have been found twice in the same location in space. FRB 121102 is located at a minimum distance of ~1150 AU away from earth, and is almost certainly extragalactic in nature. As of January 2017, FRB 121102 is believed to be co-located in a dwarf galaxy about three billion light-years from earth with a low-luminosity active galactic nucleus, or a previously unknown type of extragalactic source, or a young neutron star energizing a supernova remnant.
What is causing them remains a mystery as no consensus exists yet.
Some say it must have something to do with a supernova or merger of relativistic objects. It is suggested that hundreds of similar events could occur every day and, if detected, could serve as cosmological probes.
In 2007, just after the publication of the first discovery, it was proposed that FRBs could be related to hyperflares of magnetars. In 2015 three studies supported this hypothesis.
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 the FRBs. In 2016, the collapse of the magnetospheres of Kerr-Newman black holes are 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 FRBs originate in black hole explosions, they would be the first detection of quantum gravity effects.
A study claims there is a potential artificial origin for FRBs.
The abstract reads:
We examine the possibility that Fast Radio Bursts (FRBs) originate from the activity of extragalactic civilizations. Our analysis shows that beams used for powering large light sails could yield parameters that are consistent with FRBs. The characteristic diameter of the beam emitter is estimated through a combination of energetic and engineering constraints, and both approaches intriguingly yield a similar result which is on the scale of a large rocky planet. Moreover, the optimal frequency for powering the light sail is shown to be similar to the detected FRB frequencies. These `coincidences' lend some credence to the possibility that FRBs might be artificial in origin. Other relevant quantities, such as the characteristic mass of the light sail, and the angular velocity of the beam, are also derived. By using the FRB occurrence rate, we infer upper bounds on the rate of FRBs from extragalactic civilizations in a typical galaxy. The possibility of detecting fainter signals is briefly discussed, and the wait time for an exceptionally bright FRB event in the Milky Way is estimated.
The authors, Avi Loeb, theorist at the Harvard-Smithsonian Center for Astrophysics, and Manasvi Lingam, of Harvard University, explain FRBs might be the result of the activity of a gigantic radio transmitters built by intelligent aliens.
Loeb said in a statement on March 9, 2017:
"Fast radio bursts are exceedingly bright given their short duration and origin at great distances, and we haven't identified a possible natural source with any confidence". "An artificial origin is worth contemplating and checking."
The duo calculated that a solar-powered transmitter could indeed beam FRB-like signals across the cosmos, It would require a sunlight-collecting area twice the size of Earth to generate the necessary power.
The huge amounts of energy involved wouldn't necessarily melt the structure, as long as it was water-cooled. So, Lingam and Loeb determined, such a gigantic transmitter is technologically feasible, though beyond humanity's current capabilities.
The study explains why aliens would build such a structure: to blast interstellar spacecraft to incredible speeds. These craft would be equipped with light sails, which harness the momentum imparted by photons, much as regular ships' sails harness the wind. Humanity has demonstrated light sails in space, and the technology is the backbone of Breakthrough Starshot, a project that aims to send tiny robotic probes to nearby star systems.
A transmitter capable of generating FRB-like signals could indeed drive an interstellar spacecraft weighing 1 million tons or so, Lingam and Loeb calculated.
"That's big enough to carry living passengers across interstellar or even intergalactic distances," Lingam said in the same statement.
Humanity would catch only fleeting glimpses of the "leakage" from these powerful beams, which would be aimed at the spacecraft's sail at all times, because the light source would be moving constantly with respect to Earth, the researchers pointed out.
Scientists Michael Hipple, Wilfried F. Domainko and John G. Learned analyzed 10 of the known FRBs and ensured in 2017 that the time intervals between the highest and lowest frequencies of the detected radio pulses are all integer multiples of the same number: 187.5.
At first glance, this would imply that the FRBs are spaced regularly over billions of light years, which seems completely implausible. One might think that this is a random spacing, since only 10 FRBs were considered, but if the probability of observing such a spacing is estimated for with FRB, it seems to be less than 5 out of 10,000.
These three astronomers therefore think that these are radio sources in the Milky Way - according to them - which for an unknown reason emit high and low frequency packets spaced in time by a multiple, a fixed interval. They may be human signals, for example, from military satellites, or signals caused by extraterrestrial intelligence.
See for example https://www.newscientist.com/article/mg22630153-600-is-this-et-mystery-of-strange-radio-bursts-from-space
Hippke had submitted a paper on solar sails in javnvier 2017, readable at: https://arxiv.org/abs/1701.08803
