What caused the brightest gamma-ray burst of all time?

In October 2022, our telescopes caught something breathtaking – a cosmic flash brighter than anything we’d ever seen. This wasn’t any average starburst; it was a gargantuan gamma-ray burst (GRB), dubbed the B.O.A.T. (Brightest Of All Time) for good reason.

Fast forward a few months, and scientists using the mighty James Webb Space Telescope have cracked a big piece of the puzzle.

“As long as we have been able to detect GRBs, there is no question that this GRB is the brightest we have ever witnessed by a factor of 10 or more,” explained Wen-fai Fong, an associate professor of physics and astronomy at Northwestern’s Weinberg College of Arts and Sciences and member of CIERA.

What exactly is a gamma-ray burst?

GRBs are the most powerful explosions in the observable universe. They occur during the death of a very massive star, at least ten times the mass of our sun.

When a star this big runs out of fuel, its core can no longer support the immense pressure from its outer layers. This imbalance triggers a violent collapse inward.

As the core implodes, it crushes itself so tightly that its protons and neutrons begin to combine, forming a super-dense object called a black hole. This chaotic process releases a tremendous amount of energy.

A small portion of this energy erupts in the form of two narrow, high-speed jets that shoot out from the black hole, traveling close to the speed of light. These jets are the source of the gamma rays in a GRB.

Gamma rays are the most energetic form of light in the electromagnetic spectrum. They have much higher energy than even X-rays. Gamma rays from a GRB are extremely powerful. They can outshine all stars in a galaxy briefly.

What the B.O.A.T. gamma ray burst revealed

The B.O.A.T. was a truly extraordinary event. Its gamma-ray burst was exceptionally intense, far more powerful than those typically observed by astronomers. This immense outpouring of energy initially made it difficult to study using conventional means.

However, the James Webb Space Telescope, with its advanced infrared capabilities, was able to peer “behind the curtain” of this cosmic explosion.

This allowed scientists to uncover an unexpected feature: the presence of a supernova. Supernovas signify stars exploding and leave remnants behind from these colossal events.

Intriguingly, the supernova associated with the B.O.A.T. appears notably average in its intensity and properties. This is a stark contrast to the extreme power observed in the corresponding gamma-ray burst.

This disparity raises questions about the mechanisms that drive these events. It suggests that the sheer power of a GRB isn’t directly mirrored by the brightness of the accompanying supernova.

Where are the heavy elements?

The origin of heavy elements – such as gold, platinum, and uranium – remains one of the great unsolved mysteries of astrophysics.

These elements are essential to our understanding of the universe’s evolution and even our own existence as elements like gold play roles in our bodies.

One leading hypothesis proposes that the collapse of supermassive stars forges heavy elements in extreme environments.

These events, which result in the formation of a black hole, are often accompanied by powerful gamma-ray bursts (GRBs). Scientists hoped the B.O.A.T. would offer an opportunity to test this theory.

Unexplained absence

Using the James Webb Space Telescope’s spectroscopic instruments, scientists meticulously analyzed the light emitted from the B.O.A.T.’s supernova. They were searching for the tell-tale spectral signatures that would indicate the presence of heavy elements. Surprisingly, they found none.

This lack of evidence challenges the idea that collapsing supermassive stars are major producers of heavy elements. While alternative sources, such as the merging of neutron stars, are known to create these elements, their relative rarity suggests that there must be other, yet undiscovered, processes at play.

The search for the cosmic factories responsible for heavy element production remains a significant focus of astrophysical research.

Why was B.O.A.T. gamma ray burst so bright?

The extraordinary intensity of the B.O.A.T. has prompted several explanations. “Even several months after the burst was discovered, the afterglow was bright enough to contribute a lot of light in the JWST spectra,” said Tanmoy Laskar, an assistant professor of physics and astronomy at the University of Utah and a co-author on the study.

“Combining data from the two telescopes helped us measure exactly how bright the afterglow was at the time of our JWST observations and allow us to carefully extract the spectrum of the supernova.”

One possibility for the brightness is that the energy jets emitted from the collapsing star were highly collimated. This means they were tightly focused rather than spreading out broadly. This concentration makes the GRB appear brighter from our perspective. This is true even if the total emitted energy matches that of less-focused events.

Another potential factor lies in the B.O.A.T.’s host galaxy. Observations indicate that this galaxy is undergoing a period of intense star formation. This rapid birth of new stars suggests a very active and energetic environment.

Such conditions might play a role in influencing the properties of the supermassive stars that create GRBs, potentially making them more prone to these exceptionally powerful outbursts.

Implications of the B.O.A.T. discovery

The B.O.A.T. has provided astronomers with invaluable data, pushing forward our understanding of these extreme cosmic events and the physics behind them.

It has underscored that the sheer power of a gamma-ray burst is not necessarily a reliable indicator of the brightness of its associated supernova. This challenges previously held assumptions and forces scientists to re-evaluate the models they use to understand these phenomena.

Additionally, the lack of heavy element signatures within the B.O.A.T.’s supernova further complicates our understanding of the processes responsible for creating these elements within the universe. It suggests that even the most powerful stellar explosions might not be the primary cosmic forges for elements heavier than iron.

Furthermore, the B.O.A.T. highlights the intricate relationship between massive stars, the explosive supernovae they produce, and the dynamic environments of their host galaxies.

Studying events like this helps astronomers understand the complex processes in the universe that govern the birth, death, and evolution of stars and galaxies.

Future of gamma-ray burst research

The B.O.A.T. has ignited a renewed sense of excitement in the study of gamma-ray bursts. It has demonstrated the importance of revisiting even well-established assumptions in the field.

Advancements in observational tools, such as the James Webb Space Telescope, are ongoing. These tools equip scientists to make more remarkable discoveries.

It is an exhilarating time for astrophysicists, as they continue to assemble the pieces of this cosmic puzzle, pushing the boundaries of our knowledge about the universe.

The study is published in the journal Nature Astronomy.

Image Credit: Aaron M. Geller / Northwestern / CIERA / IT Research Computing and Data Services

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