GRB221009A

The most energetic gamma-ray burst recorded so far was observed last month and confirmed the predictions of Prof. Arnon Dar and Prof. Shlomo Dado


On October 9, 2022, the most energetic gamma-ray burst (GRB) measured so far was observed. The burst, which occurred at a distance of 2.4 billion light-years from Earth, was documented as GRB 221009A.
By chance, on October 9, 2022, an article predicting the maximum energy of GRBs, which was written by Prof. Arnon Dar and Prof. Shlomo Dado, was accepted for publication in The Astrophysical Journal Letters – the most important journal in astrophysics. The article, entitled “The Maximum Isotropic Equivalent Energy Of Gamma Ray Bursts,” predicted not only the strength of the eruption but also its other characteristics.


A gamma ray burst is a cosmic event during which a huge amount of gamma rays and X-rays is emitted within seconds in a single pulse or in several adjacent pulses. About 25 years ago, Dar and his colleagues, Prof. Ari Laor and Nir Shaviv published an article in Physical Review Letters in which they suggest the possibility that gamma-ray bursts may be responsible for some of the past major extinctions of life on Earth.


Gamma bursts were discovered in 1967, when the USA sent satellites to detect possible Soviet nuclear tests in space. Such tests were prohibited by an international agreement, but the Americans suspected that the USSR was conducting them in space on the assumption that it would be impossible to detect them from Earth due to the atmospheric absorption of x and gamma rays. Six years later, in 1973, only after it became clear that they were not caused by humans, their existence was published.


In the first two decades after the discoveries of gamma-ray bursts, most of the scientific community believed that these events were taking place in the Milky Way galaxy, which is “our” galaxy. Only in 1991 did the US National Aeronautics and Space Administration (NASA) obtained observational evidence that these events occur mainly in other, very-distant galaxies.


In 1994, Prof. Dar, together with Prof. Nir Shaviv (who was his doctoral student at the time), published a new model that explained the phenomenon – a narrow jet of balls of matter emitted at the birth of neutron stars or black holes. These balls move at a speed – close to that of the speed of light. This model became the basis of the “cannonball model” that was later developed by Profs. Dar and Dado with their colleague Prof. Alvaro De Rujula from the CERN in Geneva, Switzerland. According to this model, the balls of matter scatter the light and matter in their path, thus creating a narrow beam of high-energy photons, electrons and atomic nuclei. When the photons in the beam reach Earth, they are observed by ground and space telescopes.

In their article, Profs. Dar and Dado link the phenomenan of gamma-ray bursts to cosmic rays, which was discovered at the beginning of the last century and is a mystery that has not been solved to this day (it should not be confused with the cosmic background radiation that originated in the Big Bang). They explain that the magnetic fields in space scatter the electrons and atomic nuclei in the beam without them losing their energy. These particles become part of the so called cosmic rays which fill space.


Dado and Dar show that these two phenomena – cosmic rays and gamma-ray bursts – are probably born together in the birth of a neutron star or a black hole. Under this assumption, they estimated the maximum energy of GRBs, only slightly more than that of GRB 221009A.

On average, gamma-ray bursts are observed once daily, but bursts of the magnitude of GRB 221009A are estimated to reach Earth only once every 500 years. The burst observed on October 9th this year was measured by NASA’s Fermi Space Telescope and by an array of gamma-ray detectors that were installed in space. Its location was determined the next day using the giant VLT telescope at the Paranal Observatory in Chile.

 

The eruption report on the NASA website:
https://www.nasa.gov/feature/goddard/2022/nasa-s-swift-fermi-missions-detect-exceptional-cosmic-blast

 

Prof. Dar and Prof. Dado’s paper: https://arxiv.org/abs/2203.01942

 

Also visit:

- Interview with prof. Arnon Dar on Kan's "Three who know", available here (01:28:00 - 01:36:20).

- Media coverage on Haaretz, available here.

- Media coverage on ynet, available here.