The brightest gamma-ray burst in history turned out to be an ordinary supernova

The extremely powerful gamma ray radiation coming from deep space isGamma ray burst“It's called. Gamma-ray burst detected in 2022GRB 221009AIt attracted the attention of astronomers as the brightest gamma-ray burst in history. There has been controversy about why it is so bright, with some theories pointing to the existence of a phenomenon that cannot be explained by current physics.

A research team led by Peter K. Blanchard of Northwestern University observed the afterglow of GRB 221009A using the James Webb Space Telescope.It was determined that the true nature of the explosion was an ordinary supernova (Type II supernova).

While the source turns out to be a natural phenomenon, new mysteries have emerged. Supernova explosions are thought to produce elements much heavier than iron, but GRB 221009A, which was supposed to be an ordinary supernova explosion with no properties,No heavy elements were detectedThis was an unexpected result. The reason is a mystery, and research into GRB 221009A is likely to continue.

■ The brightest gamma-ray burst in history “GRB 221009A”

It was celebrated on October 19, 2022GRB 221009A“It is the brightest gamma-ray burst in recorded history as of April 2024. It was so bright that it could not be detected by the Fermi Gamma-ray Space Telescope, one of the major gamma-ray telescopes. In addition, after GRB 221009A occurred, a detector responded that detected the radiation Cosmic, solar wind, and lightning, an observation device unrelated to gamma ray bursts because powerful gamma rays had a significant impact on the Earth's atmosphere, with each detector causing false positives.

GRB 221009A, which was dozens of times brighter than a regular gamma-ray burst, was dubbed the “Boat (Brightest Ever),” suggesting it was the brightest in history. It is estimated that an extremely bright gamma-ray burst can only be observed on Earth once every 10,000 years, so GRB 221009A is attracting the attention of astronomers as an extremely valuable observational target.

The exact origin of gamma-ray bursts is a major mystery in astrophysics. The most likely theory is that it is related to a “supernova explosion” that occurs when a star larger 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 in which the direction of energy ejection is narrowed to a narrow band, similar to a flashlight narrowing the light to make it brighter.

In addition, because GRB 221009A was so bright, some had speculated that a phenomenon outside the current framework of physics, such as dark matter collapse, might occur. Gamma-ray bursts that are comparable to theories and simulations have not often been observed, so the mechanism is not well understood. Observations of GRB 221009A provide a valuable opportunity to test these theories.

■The real identity of GRB 221009A is an “ordinary supernova explosion”

Blanchard and other researchers closely monitored the afterglow of GRB 221009A using the Webb Space Telescope and conducted research to uncover its true nature. It is literally a lucky event that the gamma-ray burst, which was so bright that it is said to occur once every 10,000 years, appeared at a time when it would have been observed by the Webb Space Telescope, which began full-scale operation in July 2022.

However, GRB 221009A was too bright to obtain meaningful data even if it was observed immediately after its occurrence. Super bright headlights in the dark are like hiding the body of your car. Therefore, Blanchard and his colleagues determined the timing when GRB 221009A's afterglow had subsided sufficiently, and conducted observations in two separate sessions, 168 days and 170 days after its discovery.

As a result of the observations, they succeeded in capturing light (near-infrared absorption and emission spectra) indicating the presence of elements such as oxygen, calcium and nickel associated with supernova explosions, showing that there were no distinguishing features in comparison. Surprisingly,The true identity of GRB 221009A, the brightest gamma-ray burst in history, was an “ordinary supernova explosion with no characteristics.”it will be.

From this finding, “trend” may be an important reason why GRB 221009A is particularly bright. As mentioned previously, it is estimated that the energy emission from gamma-ray bursts is concentrated in a narrow band. GRB 221009A may have been observed as an extremely bright gamma-ray burst because its energy emission was perfectly directed toward Earth. However, it is also possible that GRB 221009A is particularly bright because its energy emission was concentrated in a smaller area compared to 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. Besides the fact that GRB 221009A was an explosion that occurred in the universe about 1.9 billion years ago, the star that gave rise to GRB 221009A was very heavy, contained few heavy elements, and was rotating at high speed.

By clarifying whether this estimate is correct and how often these conditions are met 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, and it may become clearer what will happen.

■A new puzzle: Heavy items cannot be found

On the other hand, on this note.Barely any heavy elements that could have been produced in a supernova explosion have been found in the afterglow of GRB 221009A.It turns out that. This is a big mystery considering the analysis results indicate that GRB 221009A is an ordinary supernova explosion.

Immediately after the birth of the universe, there were only hydrogen and helium, and elements heavier than these are known to have been created by some type of nuclear reaction. It is known that nuclear fusion reactions that occur in the cores of stars produce only heavier elements, even iron.

It is known that heavier elements are produced only in very high-energy phenomena, such as instantaneous nuclear reactions. The most well-understood situation is when very dense celestial bodies called neutron stars merge.

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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 were not sufficient for neutron star fusion, so there must be another way to produce heavy elements. Supernova explosions should have been a strong candidate for another such production pathway.

However, no heavy elements were found in the afterglow of GRB 221009A, which is supposed to be an ordinary supernova explosion, casting doubt on the relationship between supernova explosions and heavy elements. Possible hypotheses to remove this question mark are as follows.

1. The idea that GRB 221009A is an ordinary supernova explosion, as described in this study, is incorrect;
2. Supernova explosions produce far fewer heavy elements than long thought.
3. Something went wrong with the monitoring settings, and we failed to pick up heavy element signals from GRB 221009A.
4. Although the monitoring settings are correct, there is an error in interpretation of the monitoring results, and heavy metal signals are missed.

Regardless of which theory is correct, more observations are needed to prove it. The study may prompt 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 discovery of a supernova associated with GRB 221009A without r-process signature”. (natural astronomy)
• Amanda Morris. “The brightest gamma-ray burst ever recorded came from the collapse of a massive star.” (Northwestern University)

Text / Riri Ayaka Editing / sorae editorial department