15 September 2023
One of the most mysterious cosmic phenomena is fast radio bursts. These are short radio signals of an unknown nature, lasting several milliseconds, resulting from the release of a colossal amount of energy. More than a decade has passed since their discovery, but astrophysicists are still trying to figure out the mechanisms of their occurrence. The researchers name neutron stars, black holes and even transmitters of alien civilizations as possible sources. "The tape.<url>" tells about the discoveries of the past 2019, which shed light on the causes of the appearance of radio bursts.
With fast radio bursts, as much energy is released in milliseconds as the Sun emits for several tens of thousands of years. According to the leading hypothesis, they are caused by catastrophic events, such as the merger of two neutron stars, a flash during the evaporation of a black hole or the transformation of a pulsar into a black hole. For a long time it was believed that radio bursts could occur only once, but in 2015 it was discovered that the previously recorded fast radio burst FRB 121102 repeats non-periodically.
FRB 121102 is located in a dwarf galaxy three billion light-years from Earth, and for several years it remained the only known source of repeated radio bursts, despite a thorough search. However, in January 2019, an article by scientists of the Canadian CHIME collaboration appeared in the journal Nature, which reported the re—registration of signals from another source - 180814.J0422+73. Interferometric radio telescope CHIME (Eng. Canadian Hydrogen Intensity Mapping Experiment) recorded six fast radio bursts that came from a galaxy 1.3 billion light-years away.
The signals in their frequency structure and spectral characteristics resembled the signals from FRB 121102, which indicates a similar mechanism of their formation and the same nature of the source. The discovery indicates the existence of a separate type of fast radio bursts, the cause of which cannot be catastrophic events precisely because of their repeatability.
This contrasts with the repeating signal FRB 121102, which is located in the region of active star formation. Thus, single and repeated fast radio bursts should have different origins. In the case of FRB 121102, the radio signal apparently passed through a powerful magnetic field around a magnetar — a special type of neutron stars.
Soon, astronomers at the California Institute of Technology in the USA reported the discovery of another fast radio burst FRB 190523, which also occurred in a relatively calm environment — in a galaxy that is analogous to the Milky Way and is 7.9 billion light-years away from Earth.
Both of these discoveries refute that fast radio bursts can occur only in young dwarf galaxies, where there is a large number of magnetars.
ASKAP Radio Interferometer
In August 2019 in the preprint repository arXiv.org An article by the Canadian collaboration CHIME appeared, which reported the detection of eight repetitive radio signals. Two sources of radio signals — FRB 180916 and FRB 181119 — flashed more than twice (ten and three times, respectively), the others sent repeated radio signals only once, while the longest pause between the registration of radio waves was 20 hours. According to the researchers, this may indicate that in fact many FRBs are repeated, but some are more active than others.
Most of the eight new fast radio bursts showed a decrease in the frequency of the signal with each repeated flash, which may be the key to understanding the mechanism that produces these phenomena. In addition, FRB 180916 has the lowest signal dispersion indicators, indicating the relative proximity of the source to the Ground. It may also help determine the nature of the radio burst, the researchers concluded.
At the end of the summer of 2019, scientists at the National Center for Radio Astrophysics in India reported that magnetars are still one of the most likely sources of fast radio bursts (at least repetitive).
Observations of the anomalous magnetar XTE J1810-197 were conducted on the Giant Metrewave Radio Telescope. Millisecond pulses of radio emission resembling flashes from a repeating FRB 180814.J0422+73 were recorded.
Giant Metrewave Radio Telescope
This magnetar is located 10 thousand light-years from Earth. It was discovered in 2003, and in 2008 it gradually stopped emitting radio emission. However, in 2018, a new outbreak occurred on it, which also gradually began to fade. Interestingly, monitors usually do not emit radio emission, and XTE J1810-197 was the first source of radio emission of this kind. The rarity of this object, as well as repeated radio bursts, led scientists to believe that both phenomena may be related to each other.
In September 2019, Chinese astronomers reported that they had detected new repetitive fast radio bursts (FRBs) from the FRB 121102 source. The signals were detected using a 500-meter aperture FAST radio telescope with a 19-beam receiver in Guizhou Province. From the end of August to September, more than 100 bursts were recorded, which is a record number among all recorded FRBs.
By that time, scientists began to assume that FRB 121102 was a supermassive black hole, exceeding the mass of the Sun by 10-100 million times and generating a powerful magnetic field, and the direct source of the flares could be a neutron star or plasma affected by the hole. Another possible explanation is that FRB 121102 is a magnetized plerion — a nebula fueled by stellar wind from a pulsar.
Although so far fast radio bursts remain an unexplained phenomenon, in 2019, the scientific community was presented with a lot of data that brings astronomers closer to the solution. It turned out that FRBs can be repeated, and they probably do it very often. In this case, they are generated by rather exotic objects like neutron stars (pulsars and magnetars) located in a suitable interstellar medium. Single bursts occur in less turbulent conditions: galaxies, where star formation processes occur very slowly. Such phenomena, most likely, really occur due to catastrophic processes.