Fast radio bursts (FRB) are one of the most mysterious mysteries in the universe. Despite the fact that the nature of absolutely all FRBs is still unknown to astronomers, scientists seem to have finally figured out from which amazing environment some of the most discussed FRBs emerged. We are talking about repeating signals FRB 121102.
For the first time, researchers started talking about FRB 121102 signals in November 2012, but in order to narrow the search for their unusual nature, it took scientists several years. The fastest radio bursts, as a rule, appeared only once, which made the calculation of their source an impossible task, but the peculiarity of FRB 121102 turned out to be that these signals are repeated.
This gave scientists a unique opportunity to study these signals. FRBs are radio pulses lasting several milliseconds, but sometimes with the energy of 500 million suns. Since most of these radio pulses are not repeated, it becomes almost impossible to predict them. As, however, and trace their source. That is why scientists have still not been able to determine their true nature.
FRB 121102 signals have never ceased to amaze researchers for several years. In March 2016, astronomers announced the discovery of 10 fast radio bursts from the same region in archived telescope data. Six more FRB 121102 signals were detected in December 2016, and 15 more in August 2017, allowing scientists to locate the source of these signals. It turned out to be the star-forming region of a dwarf galaxy located more than three billion light-years from Earth.
An international team of researchers, studying data from different radio telescopes, was able to further narrow the search range and ultimately come to a single conclusion. Scientists are more confident than ever that a neutron star is the source of FRB 121102. And apparently, this star is in an extremely extreme environment - either very close to a black hole, or inside a very powerful nebula. The researchers were prompted to such conclusions by the fact that these radio signals were "swirling".
Experts shared their work in the journal Nature, where they report that the signals from FRB 121102 were almost completely polarized. When these polarized signals pass through a magnetic field, they twist, and the stronger the magnetic field, the more they twist. This feature is called the Faraday effect and allows researchers to learn more about the nature of certain waves. In the case of FRB 121102 signals, their plane of polarization turned out to be the most swirling ever observed, which suggests that they passed through a very powerful magnetic field.
“The only known sources in our galaxy with the same swirling plane of polarization as FRB 121102 are located in the galactic center and are located in a very dynamic region next to a massive black hole. Perhaps the source FRB 121102 is in a similar environment in its own galaxy,”says Daniel Micilli of the University of Amsterdam.
"Also, the peculiarity of the swirling plane of polarization can be explained if their source is located in a very powerful nebula left after a supernova explosion," the scientist adds.
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The observation also explains the role of the neutron star. These objects are believed to be the result of supernova explosions. If the mass of a star turns out to be higher than a certain value, then instead of a supernova it turns into a black hole.
Neutron stars are very small and very dense objects. And when they rotate, they emit radio pulses. A certain type of neutron star, called magnetars, has an extremely powerful magnetic field and is capable of generating emissions - similar to how the Sun produces solar flares. They were also considered by scientists as a possible source of fast radio pulses, but observations showed that the most powerful flares of these objects were four orders of magnitude lower in power than FRB 121102. As a result, scientists came to the conclusion that the source of FRB 121102 is a common type of neutron star. At the same time, the researchers plan to continue their work and try to find out more about the environment in which they appeared.
“We will continue to observe and track how the properties of these bursts change over time. As part of these observations, we will try to find out which of the assumptions turned out to be correct - a neutron star is located next to a black hole, or it is inside a very powerful nebula,”says Jason Hessels from the same University of Amsterdam.
At the same time, we still do not know what is the source of a dozen other observed radio bursts. They have not been repeated, as was the case with FRB 121102, so scientists suggest that FRB 121102 may be unique in its kind, while others may have different sources.
Nikolay Khizhnyak