In October 2022, an international team of researchers, including astrophysicists from Northwestern University, observed the brightest gamma-ray burst (GRB) ever recorded, GRB 221009A.

Now, a team led by Northwestern has confirmed that the phenomenon responsible for this historic burst, nicknamed the “Brightest of All Time” (B.O.A.T.), is the collapse and subsequent explosion of a massive star. The team discovered the explosion, or supernova, using NASA’s James Webb Space Telescope (JWST).

While this discovery resolves one mystery, another one emerges. The researchers speculated that evidence of heavy elements, such as platinum and gold, could reside within the newly discovered supernova. However, an extensive search did not find the signature that accompanies such elements. The origin of heavy elements in the universe continues to be one of the biggest open questions in astronomy.

When the GRB was confirmed to have been generated by the collapse of a massive star, it provided an opportunity to test a hypothesis about how some of the heaviest elements in the universe are formed. Although the team did not observe signatures of these heavy elements, this suggests that extremely energetic GRBs like the B.O.A.T. do not produce these elements. This does not mean that all GRBs do not produce them, but it is a crucial piece of information as scientists continue to understand the origins of these heavy elements.

Our images of GRB 221009A (top row), best-fit GALFIT models of galaxies (middle row) and images subtracted from the GALFIT model (bottom row). The images are shown with north up and east to the left. A clear point source is detected at the location of GRB 221009A. The red rectangle shows the orientation of the NIRSpec slit. PSF photometry of GRB 221009A was performed on the subtracted images of the galaxy. The host galaxy is well described by a single Sérsic component, although some residual galaxy structure remains in the F200W, F277W, and F444W filters.
Our images of GRB 221009A (top row), best-fit GALFIT models of galaxies (middle row) and images subtracted from the GALFIT model (bottom row). The images are shown with north up and east to the left. A clear point source is detected at the location of GRB 221009A. The red rectangle shows the orientation of the NIRSpec slit. PSF photometry of GRB 221009A was performed on the subtracted images of the galaxy. The host galaxy is well described by a single Sérsic component, although some residual galaxy structure remains in the F200W, F277W, and F444W filters. Credit: Peter K. Blanchard et al. / Nature Astronomy

The B.O.A.T. was so bright that it saturated most of the world’s gamma-ray detectors when its light reached Earth on October 9, 2022. The powerful explosion occurred approximately 2.4 billion light-years away from Earth, in the direction of the Sagitta constellation, and lasted for several hundred seconds. While astronomers rushed to observe the origin of this incredibly bright phenomenon, they were immediately struck with a sense of awe.

Instead of observing the event immediately, the researchers wanted to see the GRB during its later stages. Approximately six months after the GRB was initially detected, the team used the JWST to examine its aftermath. They found the signature of elements like calcium and oxygen typically found within a supernova, but surprisingly, it was not exceptionally bright, unlike the incredibly bright GRB that accompanied it.

After confirming the presence of the supernova, the researchers searched for evidence of heavy elements within it. However, their analysis of the infrared spectrum obtained by the JWST did not reveal any signatures of heavy elements. This suggests that events as extreme as GRB 221009A are not the primary sources of these heavy elements, which is crucial information as scientists continue to investigate the origins of the heaviest elements in the universe.

The researchers believe that the extreme brightness of the B.O.A.T. may be related to the structure and shape of the relativistic jets produced by the rapidly rotating, collapsing massive star. These narrow, focused jets can produce a more intense and brighter beam of light, similar to the focused beam of a flashlight compared to a wide-spreading beam.

Additional clues may come from future studies of the host galaxy where the B.O.A.T. occurred, as the spectrum of the galaxy suggests an intense star-forming environment, which could be different from previous GRB events.


Sources

Nortwestern University | Blanchard, P.K., Villar, V.A., Chornock, R. et al. JWST detection of a supernova associated with GRB 221009A without an r-process signature. Nat Astron (2024). doi.org/10.1038/s41550-024-02237-4


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