In October 2022, an international team of researchers, including University of Utah astrophysicist Tanmoy Laskar, observed the brightest gamma-ray burst (GRB) ever recorded, GRB 221009A.
Now, physicists have confirmed that the phenomenon responsible for the historic burst—dubbed the B.O.A.T. (“brightest of all time”)—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 solves one mystery, another mystery deepens. The researchers speculated that evidence of heavy elements, such as platinum and gold, might reside within the newly uncovered supernova. The extensive search, however, did not find the signature that accompanies such elements. The origin of heavy elements in the universe continues to remain one of astronomy’s biggest open questions.
Tanmoy Laskar, co-author of the study that was published in Nature Astronomy on April 12, spoke with AtTheU about why GRB 221009A was the B.O.A.T.
PHOTO CREDIT: International Gemini Observatory/NOIRLab/NSF/AURA/B. O'Connor (UMD/GWU) & J. Rastinejad & W Fong (Northwestern)
The research teams hypothesize that the record-breaking burst (marked above) was generated by a massive star collapsing and giving birth to a black hole.
Download Full-Res ImageWhat exactly is the B.O.A.T.?
In October 2022, space satellites found a brilliant flash of gamma rays from a new gamma-ray burst. Gamma-ray bursts are the most powerful, violent explosions in the known universe. We have seen gamma-ray bursts before, but this one was so bright that its light blinded our gamma-ray telescopes in space and even shook the Earth’s upper atmosphere! Several dedicated people worked very hard to reconstruct the original gamma-ray signal and found that this gamma-ray burst was by far the brightest of all time (B.O.A.T) we have ever recorded. It has been exciting to study the B.O.A.T. over the last couple of years to try to figure out two big mysteries: What kind of star is responsible for this powerful light display, and what produces the heavy elements in the universe?
How can finding a supernova help in solving these mysteries?
There are two theories as to what makes these powerful, gamma-ray bursts—one is the collapse of massive stars at the ends of their lives (which also results in an explosion of the star as a supernova), and the other is a merger of two neutron stars, which are dense remnants of dead stars. We looked for the signature of a supernova, which would definitively tell us which theory was responsible for the B.O.A.T. explosion.
The other reason we wanted to search for the supernova was to solve the mystery of what produces heavy metals. Supernovae are factories that manufacture many elements in the universe—could a supernova powerful enough to create the gamma-ray burst also produce heavy elements in the explosion, like platinum and gold?
PHOTO CREDIT: Kelby Hahn
Tanmoy Laskar, assistant professor, Department of Physics & Astronomy, University of Utah
Download Full-Res ImageDid you detect a supernova?
Yes! To find the supernova, we had to wait several months for conditions to be right. Gamma-ray bursts have powerful jets, and when these jets crash into the surrounding material, they light up brightly at all wavelengths of light, from radio waves to X-rays. This is called the afterglow. The afterglow from a gamma-ray burst can shine for years and can make it difficult to see anything specific going on. Once the afterglow faded, Dr. Peter Blanchard at Northwestern University led the international effort. We took a spectrum in infrared light using JWST that would tell us what elements were present in the explosion. The spectrum showed signatures of calcium and oxygen, just like we expected for a supernova, and this gave us definitive proof that the explosion came from the death of a massive star. One mystery solved!
Did you find evidence for the heavy elements?
No, we did not find any signatures of heavy elements. This seems to be telling us that supernovae of the type associated with gamma-ray bursts likely do not make heavy elements in significant quantities. So then, what produces heavy metals? That’s still a mystery. But I should say that this is only one such case and is still early to tell if this is universally true.
PHOTO CREDIT: Aaron M. Geller / Northwestern / CIERA / IT Research Computing and Data Services
The artist’s visualization of GRB 221009A shows the narrow relativistic jets (emerging from a central black hole) that gave rise to the gamma-ray burst and the expanding remains of the original star ejected via the supernova explosion.
Download Full-Res ImageWhy did you need to use JWST for this work?
There are three reasons. The first is that several months after the explosion when we had the best conditions to study, the supernova had cooled so that the light naturally came out at infrared wavelength. Second, the signatures of heavy elements are also expected to show up most strongly in the infrared. The final reason is mostly pragmatic—it turns out by unlucky coincidence that there is a lot of dust in our galaxy in the part of the sky where this burst was located, and that dust blocks visible light. Infrared light is less affected by dust, so looking at the burst in infrared light can give us a stronger signal and more reliable information. JWST is the world’s best telescope for observations at infrared wavelengths, so it was a natural choice for this study.
Is it surprising that this supernova was faint compared to its gamma-ray burst?
Yes, one of the biggest questions is why the burst of gamma rays was so bright when the supernova was fairly ordinary. One possible answer is that the jets that powered the gamma-ray burst and its afterglow are very narrow. Narrow jets would make the burst and afterglow appear very bright. There are hints that this might be the case, but we need some more data to be sure. We are still observing the afterglow using X-ray telescopes, where we think we might have a very good shot at figuring out how narrow the jets from this burst were, and that should help settle this mystery!
Intro adapted from a Northwestern article written by Amanda Morris.
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Lisa Potter
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949-533-7899 lisa.potter@utah.edu