Extremely powerful gamma ray radiation from distant space isgamma ray burst” is called. Gamma-ray burst observed in 2022GRB221009A” attracted the attention of astronomers as the brightest gamma-ray burst in history. There has been some debate as to why it was so bright, with some theories suggesting that it was a phenomenon that could not be explained by existing physics.
A research team led by Peter K. Blanchard of Northwestern University observed the afterglow of GRB 221009A with the James Webb Space Telescope.It was determined that the true nature of the explosion was a normal supernova explosion (type II supernova).
Although the source turns out to be a normal phenomenon, new mysteries have emerged. Supernova explosions were thought to produce elements much heavier than iron, but GRB 221009A, which should have been a normal featureless supernova explosion,Heavy elements not detectedThis was an unexpected result. The reason is a mystery and research into GRB 221009A is likely to continue.
[▲Figura1:RappresentazioneartisticadelGRB221009A.(Credito:AaronM.GellerNorthwesternCIERAITResearchComputing&DataServices)]
■The brightest gamma-ray burst in history “GRB 221009A”
Observed on October 19, 2022GRB221009A‘ is the brightest gamma-ray burst ever recorded in history in April 2024. It was so bright that it could not be detected by the Fermi Gamma-ray Space Telescope, one of the leading gamma-ray telescopes. In addition, after the occurrence of GRB 221009A, a detection device that detects cosmic rays, solar wind and lightning took place, which is an observation device unrelated to gamma-ray bursts. This is because powerful gamma rays had such an impact on Earth’s atmosphere that every detection device caused false positives.
GRB 221009A, which was dozens of times brighter than a normal gamma-ray burst, was nicknamed “BOAT (Brightest Of All Time),” indicating that it was the brightest in history. It is estimated that such an extremely bright gamma-ray burst can be observed on Earth about once every 10,000 years, so GRB 221009A is attracting the attention of astronomers as a very valuable observational target.
The exact origin of gamma-ray bursts is a great mystery in astrophysics. The most likely theory is that it is linked to a “supernova explosion” that occurs when a star more massive than the Sun reaches the end of its life. If so, converting all of the star’s mass into energy is not enough. Therefore, a phenomenon is thought to occur where the direction of energy output is narrowed to a narrow range, similar to a flashlight narrowing the light to make it brighter.
Furthermore, because GRB 221009A was so bright, some predicted that a phenomenon beyond the current framework of physics would occur, such as the collapse of dark matter. Gamma-ray bursts that can be compared with theories and simulations have not been observed very often, so the mechanism is not well understood. The observations of GRB 221009A provide a valuable opportunity to test these theories.
[▲Figura2:GRB221009Afotografatoall’OsservatorioGemini.(Credito:OsservatorioInternazionaleGeminiNOIRLabNSFAURAB.O’Connor(UMD/GWU)eJ.RastinejadeWFong(Nordovest))]
■The true identity of GRB 221009A is “an ordinary supernova explosion”
Blanchard and other researchers closely observed GRB 221009A’s afterglow with the Webb Space Telescope and conducted research to discover its true nature. It is literally a lucky event that the gamma-ray burst, so bright it is said to occur once every 10,000 years, appeared at a time when it could be observed by the Webb Space Telescope, which began full-scale operation in July 2022.
However, GRB 221009A was so bright that no significant data could be obtained even when observed immediately after its occurrence. Headlights that are too bright in the dark are like hiding the bodywork of your car. Therefore, Blanchard and his colleagues determined the time when GRB 221009A’s afterglow dimmed sufficiently and conducted observations in two separate sessions, 168 days and 170 days after its discovery.
As a result of the observations, they managed to capture light (near-infrared absorption and emission spectra) indicating the presence of elements such as oxygen, calcium and nickel associated with the characteristic supernova explosions in comparison. surprisingly,The true identity of GRB 221009A, the brightest gamma-ray burst in history, was “an ordinary featureless supernova explosion”Will be.
From this result, “direction” could be an important reason why GRB 221009A was particularly bright. As mentioned above, the energy output of gamma-ray bursts is estimated to be concentrated in a narrow range. GRB 221009A may have been observed as an extremely bright gamma-ray burst because its energy output was perfectly directed towards Earth. However, GRB 221009A may have been particularly bright because its energy output was concentrated in a smaller area than other gamma-ray bursts.
This observation also revealed that the galaxy to which the exploded star belongs is characterized by a lack of heavy elements. Considering the fact that GRB 221009A was an explosion that occurred in the universe approximately 1.9 billion years ago, the star that gave rise to GRB 221009A is extremely heavy, has few heavy elements, and is estimated to rotate at high speed. .
By clarifying whether this estimate is correct and how often these conditions occur throughout the universe, we will be able to understand how rare extremely bright gamma-ray bursts like GRB 221009A are and what the mechanism is. It may become clear what will happen.
■A new mystery: heavy elements cannot be found
On the other hand, in this observation,Almost no heavy elements that would be produced in a supernova explosion were found in the afterglow of GRB 221009AIt turns out that. This is a big mystery, considering the analysis that GRB 221009A is a normal supernova explosion.
Soon after the birth of the universe practically only hydrogen and helium existed, and it is known that the heavier elements of these were created by some type of nuclear reaction. Of these, nuclear fusion reactions that occur in the core of stars are known to produce only the heaviest elements, up to iron.
It is known that heavier elements are produced only in very high energy phenomena, such as instantaneous nuclear reactions. The best known situation is when neutron stars, which are very dense celestial bodies, merge together.
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But it takes billions of years for neutron stars to form and get close enough to collide with each other. In fact, heavy elements were found even in the early Universe, when conditions would not have been sufficient for the merger of neutron stars, so there must be another way to produce heavy elements. Supernova explosions were supposed to be a strong candidate for another production path.
However, no heavy elements were found in the afterglow of GRB 221009A, which is expected to be a normal supernova explosion, casting doubt on the link between supernova explosions and heavy elements. Possible hypotheses for removing this question mark include the following.
1. The idea that GRB 221009A is a normal supernova explosion, as shown in this study, is incorrect: it actually has some unique properties;
2. Supernova explosions produce far fewer heavy elements than long believed.
3. There is something wrong with the observation settings and we are unable to capture heavy element signals from GRB 221009A.
4. Although the observation settings are correct, there is an error in the interpretation of the observation results and the heavy element signals are missing.
Regardless of which theory is correct, further observations are needed to prove it. The study could motivate the Webb Space Telescope to observe bright gamma-ray bursts associated with common supernova explosions, such as GRB 221009A.
Source
- Peter K. Blanchard, et al. “JWST detection of a supernova associated with GRB 221009A without r-process signature”. (Natural Astronomy)
- Amanda Morris. “The brightest gamma-ray burst of all time came from the collapse of a massive star.” (Northwest University)
Text/Riri Ayaka Edit/sorae Editorial Department
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