Astronomers have long been haunted by the mystery of the birth of fast radio bursts – short and bright bursts of radio emission that appear somewhere in space and have an unclear nature. Now scientists have finally figured out their source. It is especially pleasant that Russian experts have made an important contribution to this.
The achievement is described in two scientific articles published in the journal Nature Astronomy. The first of them was written by Russian scientists with the participation of one researcher from the United States. The second belongs to the pen of Chinese astronomers.
Fast radio bursts (FRB) are short (several milliseconds in duration) and bright bursts of radio emission. They were first discovered in 2007 and have been observed about a hundred times since then. But the nature of these outbreaks remained a mystery, although there were many hypotheses.
Back in 2007 Konstantin Postnov and Sergey Popov from the State Astronomical Institute named after P.K.Sternberg, Moscow State University named after M.V. Lomonosov, put forward an interesting hypothesis. They suggested that magnetars are the source of FRB. These are neutron stars with a colossal magnetic field: 1013–1014 Gaussian. For comparison: the earth’s magnetic field has a magnetic induction of less than one gauss.
By the way, magnetars are rare birds: only about thirty of them are known in the entire vast galaxy.
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April 18, 2020 radio telescopes for the first time fixed FRB, born in the Milky Way (FRB 200428 as it was named). Astronomers identified the celestial body that emitted this radio pulse, and it really turned out to be the SGR 1935 + 2154 magnetar. This became a milestone in the history of the study of fast radio bursts. One of the most authoritative scientific journals in the world – Science – included this discovery in the list of the most important scientific breakthroughs of 2020.
However, meticulous scientists still had some doubts that the source of the radio pulse was determined correctly. Now they have disappeared. All thanks to the observations of the magnetar SGR 1935 + 2154 in X-rays and gamma rays.
Just in April 2020, this celestial body showed a particularly violent activity. X-ray and gamma-ray flares followed one another. Another such event took place on April 28, simultaneously with the fast radio burst FRB 200428. The X-ray pulse pattern exactly repeated the radio burst: two millisecond peaks separated by an interval of 30 milliseconds. There is no doubt that the source of the X-ray flare was precisely SGR 1935 + 2154: the coordinates were determined even more accurately than in the radio range.
Two simultaneous and exactly the same flashes in radio waves, X-rays and gamma rays cannot be a coincidence. Undoubtedly, they were generated by the same event on the SGR 1935 + 2154 magnetar.
Note that FRB 200428 was the first fast radio burst recorded in a range other than radio waves.
X-ray and gamma-ray observations were carried out at once by several orbiting telescopes. These are the Russian instrument “Cone” aboard the American Wind Observatory, as well as telescopes Integral (European Space Agency), Agile (Italy) and Insight-HXMT (China).
By the way, the flare that accompanied the FRB 200428 radio burst was not at all similar to the usual X-ray flares of the magnetar. Apparently, in order for a fast radio burst to be born, something special must happen to the neutron star. This explains why such events have not been recorded in our galaxy for so long.
“The simultaneous registration of a burst from a galactic magnetar, which is quite similar to a fast radio burst FRB, in the radio and X-ray / gamma ranges of the spectrum is the strongest argument in favor of the magnetar hypothesis [происхождения быстрых радиовсплесков], and also allows us to say that at least a significant fraction of fast radio bursts is generated by powerful flares of extragalactic magnetars “, – summarizes co-author of the scientific article Sergey Popov.
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Neutron stars with super-strong magnetic fields are the source of mysterious radio bursts.
Let us explain that astronomers call galactic objects located in the Galaxy (that is, in the Milky Way), and extragalactic ones – those lying outside it.
Let’s pay attention to the scientist’s caution: he says not “all fast radio bursts” but “at least a significant fraction of fast radio bursts”. Astronomers have long known that phenomena that are very similar from the point of view of an observer sometimes have very different natures. So it cannot be ruled out that magnetars generate only part of the FRB, while the rest of the flares are generated by something else.
By the way, caustic experts still have one more reason to doubt: the total energy released during the FRB 200428 radio burst is ten times less than that of radio bursts observed in other galaxies. However, scientists have a hypothesis that gracefully explains this fact. They assume that radio bursts come in very different strengths. Weak bursts occur more often, but, naturally, only the strongest are visible at intergalactic distances. So there is nothing surprising in the fact that the first FRB discovered in the Milky Way was weak (they happen more often), while in other galaxies only strong ones are observed (we simply cannot see the rest from such a distance).
“Now theorists have to understand what is the mechanism of FRB occurrence in detail. And observers continue to observe in the hope of finding new clues to better understand the mystery of fast radio bursts,” Popov notes.
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