MOSCOW, June 23, Tatiana Pichugina. Last year, scientists discovered the super-bright gamma-ray burst GRB 221009A with extreme properties. Recently, a group of researchers, including astrophysicists from Moscow State University, described it in detail. This work, according to experts, will help to find the source of the most powerful explosions in the universe.
Echo of an explosion of stars
Gamma-ray bursts were discovered in the late 1960s by American military satellites with X-ray and gamma-ray detectors. A few years later, the data was declassified. Soviet satellites have also observed this.
Telescopes see gamma-ray bursts as a very fast emission of photons, exceeding the background values in space and all known sources of energy in the Universe in terms of power. The flashes are an order of magnitude brighter than the total luminosity of the Milky Way, but where they come from is still unknown, although scientists are getting closer to unraveling.
For a long time, astronomers believed that gamma-ray bursts were born in our Galaxy. And only two decades later it became clear — they are much further. In addition, some originated 13 billion years ago in the early universe. How strong must the explosion be so that the light does not die out during such a long journey through outer space? Experts give an explanation: a gamma-ray burst accompanies the appearance of a very massive, but compact space object — such as a black hole.
First time in history
Ordinary gamma-ray bursts last a fraction of a second, a second or two at most. In the late 1990s, astronomers began to record longer bursts that, judging by recent data, accompany a hypernova — the name given to a very large supernova formed after the collapse of the core of a supermassive star. Short gamma-ray bursts more often indicate the merger of two neutron stars. In both cases, black holes appear.
In early October 2022, instruments aboard the Fermi space observatory and other orbiters recorded an unprecedentedly bright gamma-ray burst that lasted five minutes. The astronomical community was alerted to the event, and many telescopes were pointed at coordinates in the sky to see the phenomenon in a wide range of electromagnetic radiation. It turned out that nothing brighter had yet been discovered in more than half a century of gamma-ray observations.
Among those who withstood the light «strike» were the Russian Konus instruments aboard the NASA Wind spacecraft, as well as the ART- XC as part of the Spektr-RG space observatory. » data-crop-width=»600″ data-crop-height=»828″ data-source-sid=»» class=»m-vertical lazyload» lazy=»1″ />
The anomalously powerful gamma-ray burst has been designated GRB 221009A and is now being carefully studied. In the Laboratory of Experimental Astrophysics of the A.F. Ioffe Physical-Technical Institute of the Russian Academy of Sciences, which is responsible for the Cone experiment, they calculated: GRB 221009A carries a colossal energy of 1055 erg, which is equivalent to more than six and a half rest masses of the Sun.
< br />The ART-XC telescope, which observed the flare not «head on», recorded a 600-second pulse: four peaks, and then a smooth decline. Moreover, the detectors of the «Cone» monitored the extinction of the burst for more than seven hours. In general, the afterglow of GRB 221009A was observed for another three months.
Thousands of photons traveling with an energy of 18 teraelectronvolts (TeV) were captured in GRB 221009A. Never before has anything like this been found in gamma-ray bursts. Only the latest generation of accelerators is capable of accelerating elementary particles to such an energy.
There are various hypotheses explaining this phenomenon, including the decay of heavy neutrinos and hypothetical axions. However, it remains a mystery how gamma rays could not lose energy on their way to us.
«This is the echo of an explosion. A relativistic flow of huge energy flies through the interstellar medium and slows down, loses kinetic energy. In front of it is a shock wave that produces these accelerated high-energy particles,» Doctor of Physical and Mathematical Sciences Professor Vladimir Lipunov described the nature of the gamma-ray burst , founder of the network of robotic telescopes MASTER SAI MSU. Instruments of this network in South Africa and Argentina observed GRB 221009A in the optical range and were the first to indicate an unusual afterglow. In June, an article with results obtained, including by MASTER robotic telescopes, was published in Science Advances.
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The rarest event
Having processed a large amount of data from different detectors, the scientists built a scheme for the GRB 221009A jet (the so-called plasma jet flowing from the nuclei of active galaxies). And they came to the conclusion that it is directed towards the Earth — this is precisely what explains its anomalous brightness. «It's like directing a garden hose with water straight at us,» the press service of the University of Bath (UK) quotes Hendrick Van Erten, co-author of the article. Apparently, the jet took with it a large amount of stellar material. Therefore, it has a wide cone with no visible edges, whereas a jet usually looks like a narrow isolated jet.
The unusual cone of the gamma-ray burst allowed scientists to see its complex structure and depth, where the luminosity of a particular wavelength changes over time. According to the calculations of the authors, the formation of such a structured jet required somewhat less energy than in the standard case — 4 * 1053 erg of energy.
Using the structured jet model, experts calculated that such a superbright event can be observed only once in a thousand years. Its exceptional rarity is also indicated by the unusually small redshift of GRB 221009A — 0.1505. This value characterizes the distance of the radiation source from the observer, in this case, approximately 2.4 billion light years. That is, it is also one of the closest super-powerful gamma-ray bursts to us. The search for its source continues.