A team of researchers scrutinizing the brightest gamma-ray burst in at least 10,000 years identified a unique emission line that it believes could reveal some extreme physics at the heart of the burst.
The team’s research, published this week in Science, interrogates an emission line that appeared about 280 seconds after the gamma-ray burst began.
“When I first saw that signal, it gave me goosebumps,” said Maria Edvige Ravasio, a researcher at Radboud University in the Netherlands and lead author of the research, in a NASA release. “Our analysis since then shows it to be the first high-confidence emission line ever seen in 50 years of studying GRBs.”
What was this gamma-ray burst?
The gamma-ray burst was a particularly huge space explosion thought to be caused by the brilliant death of a distant star. Its full name is GRB 221009A, but it’s more commonly known as the BOAT, or the Brightest Of All Time. That’s not literally true, but it’s definitely the brightest that’s ever been recorded.
The burst contains a trove of information about the star’s collapse, so brilliantly delivered that the X- and gamma-rays temporarily overwhelmed most space-based observatories. But nearly two years since the event, researchers are still learning new information about the BOAT.
“While some previous studies have reported possible evidence for absorption and emission features in other GRBs, subsequent scrutiny revealed that all of these could just be statistical fluctuations. What we see in the BOAT is different,” said Om Sharan Salafia, a researcher at INAF-Brera Observatory and co-author of the paper, in the same release. “We’ve determined that the odds this feature is just a noise fluctuation are less than one chance in half a billion.”
A brief history of the BOAT
The BOAT was first spotted by the National Science Foundation’s NOIRLab telescope Gemini South in October 2022. Researchers determined the event occurred about 2.4 billion light-years away, and space-based X- and gamma-ray telescopes were quickly overwhelmed by the brilliance of the event.
The event was confirmed as the BOAT in March 2023. The burst is not actually the brightest of all time, but “likely the brightest burst at X-ray and gamma-ray energies to occur since human civilization began,” as one astrophysicist said. The BOAT was determined to be a one-in-10,000-year event. A research team published its X-ray observations of the burst in The Astrophysical Journal Letters.
That June, another team analyzed the structure of the BOAT’s gamma ray jet. The astronomers believe the structure of the burst could provide a blueprint to understand gamma ray bursts from other bursts of energy spewed by collapsing stars.
Researchers published a more complete analysis of the BOAT’s gamma-ray energy output in November 2023. That work found the star that bore the BOAT was 20 times heavier than the Sun, and the burn lasted hundreds of seconds. Ultimately, the team identified over 140 gamma-rays in the event that exceeded 3 teraelectronvolts. The finding “challenges the standard model of GRB afterglows,” one researcher told Gizmodo.
What did the researchers find?
The emission line spotted by the team persisted for about 40 seconds, with a peak energy of about 12 million electronvolts. The research team believes it was caused by collisions between electrons and positrons—their antimatter counterpart.
“When an electron and a positron collide, they annihilate,” said study co-author Gor Oganesyan, a researcher at Gran Sasso Science Institute and Gran Sasso National Laboratory, in the same release. “Because we’re looking into the jet, where matter is moving at near light speed, this emission becomes greatly blueshifted and pushed toward much higher energies.”
According to the NASA article, in order to have the peak energy observed by the team, the electron-positron pairs must have been traveling towards us at 99.9% the speed of light. The BOAT’s extreme explosiveness was already well-known, but the new research puts that dynamism into perspective.
What now for the BOAT?
Scientists are still sifting through the explosive aftermath of the 2022 explosion. Just this April, a team used the Webb Space Telescope to study the burst’s origin and found it was caused by a supernova: a star’s brilliant, explosive death. The team saw no signs of heavy elements from the BOAT, leaving the origins of those elements in the universe an open question.
Further study of the BOAT’s fallout and continued observations of other gamma-ray sources could shed light on these events, some of the most intense in our universe.
