With the help of data from the James Webb Space Telescope, researchers have finally solved the mystery of BOAT (Brightest of All Time), the biggest cosmic explosion since the Big Bang.
BOAT, as the English translation of the abbreviation shows, was the brightest gamma-ray burst of all time (gamma-ray burst, GRB), and it probably took approx. A supernova explosion occurring at the death of a massive star 2 billion light-years away is responsible. The process involving the powerful light phenomenon may have resulted in the birth of a black hole.
However, with the unraveling of the cosmic mystery, additional unanswered questions arose: during a supernova explosion accompanied by a GRB, heavy elements similar to gold and platinum are also produced, but the researchers did not find any traces of them anywhere.
The leader of the research, Peter Blanchard, commented on the newly achieved results of his group as follows: “We have now witnessed an event that happens once every 10,000 years: photons hit our gamma-ray detection instruments with such high energy as never before. When it was confirmed during our research that the GRB was created by the explosion of a massive star, we thought that by examining the phenomenon we would have an excellent opportunity to learn more about the formation of the heaviest elements in the Universe. However, contrary to our expectations, the presence of these elements in the system was not detected. Based on this, we came to the conclusion that high-energy gamma-ray bursts similar to BOAT do not necessarily produce the mentioned heavy elements.”
The brightest GRB of all time
The BOAT event, originally known as GRB 221009A, was detected on October 9, 2022, and with its extreme brightness, it immediately stood out from other gamma-ray bursts. After detecting the high-energy gamma rays, the researchers observed several fainter afterglows at different wavelengths of electromagnetic radiation. The event was first recorded by gamma and X-ray telescopes, and researchers immediately began searching for a possible source of the eruption in the direction of the constellation Sagittarius.
“This one was the brightest GRB ever detected, and it was about 10 times as bright as previous ones.” said one of BOAT’s explorers. However, Blanchard’s group did not hurry to publish the study of the extraordinary event, but instead observed the fading of the brightness of the gamma-ray burst. More than half a year after the first detection, the mirrors of the James Webb Space Telescope were directed towards the fading GRB in order to examine it in more detail.
“The GRB was so bright that in the first months after the outburst it completely obscured any recognizable signs of its source supernova explosion.” Blanchard explained. – “I would compare the afterglow, which can be observed at several wavelengths, to the headlights of an oncoming car, which prevents us from seeing the oncoming car itself. That’s why we had to wait for this cosmic light to fade significantly in order to catch a glimpse of the supernova.”
Using the James Webb Space Telescope’s near-infrared NIRSpec spectrograph, the team was able to examine BOAT’s infrared afterglow and detect the presence of calcium and oxygen, which are often produced during supernova explosions, in the spectra. What turned out to be surprising, however, was that the supernova explosion that produced the brightest gamma-ray burst of all time turned out to be average.
“It was no brighter than supernovae that produced less luminous GRBs.” Blanchard said. – “We would expect to observe a suitably bright supernova at the site of such a high-energy gamma-ray burst, but this was not the case in this case: we saw an average supernova at the time of the extremely bright GRB.”
It is still a mystery how an “ordinary” supernova can create a GRB that releases such enormous energy. The researchers believe that the source of BOAT’s brightness lies in the shape and structure of the jet flowing along the poles of the black hole created when the core of a massive star explodes as a supernova. The faster the collapsing star rotates, the narrower and, consequently, the brighter the beam that flows out of it at nearly the speed of light. This is consistent with the experience that astronomers thought they saw an exceptionally narrow jet in the case of BOAT. In addition to the rapid rotation, of course, other phenomena may have contributed to the GRB’s outstanding brightness.
What also raises questions about the phenomenon is the lack of heavy elements in the analyzed scenes.
The mystery of the missing elements
The interior of stars resembles the shell structure of an onion: the outer shells contain lighter elements and the inner shells contain heavier elements. However, even in the case of the most massive stars, the fusion processes only take place until iron with a mass number of 56 is formed. Elements heavier than iron, such as gold or platinum, can be formed during even higher-energy processes, such as the fusion of neutron stars. The James Webb space telescope also plays a big role in proving this theory. Another idea of the researchers for the formation of elements heavier than iron lies in the processes taking place during high-energy supernova explosions capable of creating GRBs. By themselves, merging neutron stars would not be able to create as many heavy elements as we can observe in the Universe.
According to Blanchard, it takes a long time for neutron stars to merge: the members of a binary star system must first explode as a supernova to leave behind a neutron star as a remnant. After that, it takes billions of years for the two stars to finally merge as they get closer and closer to each other. In contrast, there were already heavy elements in the early Universe, even before the first neutron stars had fused. That is why other processes probably play a role in the formation of heavy elements. Such a process can be, for example, the explosion of the high-mass, rapidly rotating stars that also created BOAT.
Using data from JWST, Blanchard’s research team got a glimpse into the inner regions of the exploding star, where elements heavier than iron are theorized to form. “During a supernova explosion, the expanding shock wave material is initially opaque. said the researcher. – “But as the remnant expands and cools more and more, it becomes more and more transparent, and thus we can gain insight into the ever deeper layers of the star. In addition, the different chemical elements absorb and emit photons at different wavelengths of the spectrum, so they can be clearly identified in the color image made of them. This means that by observing the color image of an object, we can reveal its chemical composition. However, to our great surprise, we did not see any signs of elements heavier than iron when examining the spectrum of BOAT. From this, we conclude that extreme events like GRB 221009A are not the primary source of the formation of heavy elements. This realization is crucial for studying the formation of heavy elements.”
However, according to Blanchard, the failure to detect heavy elements in BOAT’s environment does not mean that the supernovae that create GRBs cannot create such elements, so their investigation is still important. It is not necessary that these elements can form in the environment of every GRB, it is enough if this happens only in a few cases. However, further measurements with the James Webb Space Telescope are needed to fully understand the process.
The study on the results described here was published in the prestigious journal Nature Astronomy on April 12.
Source of the article:
https://www.space.com/boat-brightest-cosmic-blast-of-all-time-source-massive-star-death
