In this artist’s impression, a jet is produced by an unusually bright gamma-ray burst.
NASA/Swift/Cruz deWilde
An explosion — about 100 times brighter than previously recorded — blinded scientists’ instruments.
Scientists marveled at the power of the gamma-ray jet, which likely marked the birth of a black hole.
The explosion may have been so bright because it was powered by a unique jet structure.
The brightest gamma-ray explosion ever caught on record, which was so bright it blinded scientific instruments, just got weirder.
GRB 221009, first spotted in October 2022, outshone other cosmic explosions on record by “not just a little bit, but a hundred times,” George Washington University graduate student Brendan O’Connor said in a press release.
The explosion earned the nickname BOAT for “Brightest of All Time.”
Astronomers have since been trying to work out what could have made the gamma-ray burst so bright, and may finally have an answer.
Researchers have discovered that the gamma-ray explosion ejected a jet with an unusual structure which dragged a large amount of stellar material along with it. The discovery, the say, could shed new light on the origins of the universe.
Gamma-ray bursts shed light on the origins of stars
A picture of the galaxy that encompasses the BOAT, taken by Hubble between November and December last year. The BOAT is circled with a purple circle.
NASA, ESA, CSA, STScI, A. Levan (Radboud University); Image Processing: Gladys Kober
Gamma-ray bursts (GRBs) are hugely powerful explosions, releasing more energy into the universe in a few seconds than our sun expands over the course of its lifetime.
They happen at the birth of black holes, when a supermassive star collapses in on itself releasing powerful jets of matter that can be spotted millions of light years away. An animation below shows how this works:
Thanks to their brightness, scientists can observe these bursts “all the way back to the first stars,” O’Connor said.
“As we begin to probe this really high redshift, very distant, gamma-ray bursts, we can learn about how stars first formed, what environment they’re forming in, what type of elements were existing at these times, and see how this star formation actually evolved over the history of the universe,” he said.
Scientists have spotted about 10,000 of these gamma-ray bursts since the 70s. But this particular burst was relatively close, coming from a star about 2.4 million light-years away, which gives us an unprecedented look into the structure of these bizarre explosions.
“It’s a hugely different event, and based on the brightness and its proximity to us, we expected it to be a once-in-a-century event,” said O’Connor.
BOAT was particularly weirdA jet of particles pierces a star as it collapses into a black hole during a typical gamma-ray burst, as depicted in this artist’s concept. The jet created by gamma-ray burst 221009A had some unique features.
NASA’s Goddard Space Flight Center
We don’t see the explosion from gamma-ray bursts directly. Instead, we see the gamma rays and other rays like X-rays coming off the jet of hot gas released by the explosion, which we’re usually only lucky to see if they’re aiming straight at our planet.
The jet itself is usually over in a matter of seconds, but scientists can capture its afterglow, which drags stellar material behind it. This fades quickly, but the BOAT’s afterglow lingered much longer than usual, puzzling scientists.
A new analysis studying the explosion, published in the peer-reviewed journal Science Advances, explains why.
Scientists had typically thought these jets were always “shaped like ice cream cones,” Alexander van der Horst, associate professor of physics at George Washington University and study-co author, said in a press release.
This mean they tend to be compact and very directed, spreading out neatly through the universe, with the afterglow dragging behind the first wave.
But the new analysis suggests that the BOAT jet was sloppier, spreading out from a “narrow core with wider, sloping sides,” NASA said in a press release.
“Our work clearly shows that the gamma-ray burst had a unique structure, with observations gradually revealing a narrow jet embedded within a wider gas outflow where an isolated jet would normally be expected,” Hendrik Van Eerten, a physicist at the University of Bath and study co-author, said in a press release.
BOAT subverted expectations
Observations made two and five days after GRB 221009A erupted show data collected in the afterglow of the jet
ESA/XMM-Newton/M. Rigoselli (INAF)
What scientists think happened is that, as the jet was being expelled, it mingled with stellar material which messed with its outflow.
“The only way to produce a different jet structure and vary the energy is to vary some property of the star that exploded, like its size, mass, density, or magnetic field,” said Eleonora Troja, a professor of physics at the University of Rome, who led NuSTAR the observations of the event.
“That’s because the jet has to basically force its way out of the star. So, for example, the amount of resistance it meets would potentially influence the features of the jet.”
This is “exciting” because “we have no way of studying the star that produced this event; it’s gone now. But we now have some data giving us clues about how it exploded,” said O’Connor, who was an author on this study.
The analysis demonstrates that the most extreme explosions do not obey the standard physics assumed for normal gamma-ray bursts, he said.
Van Eerten agrees: “Our model helps not just to understand the BOAT, but also previous brightness record holders that had astronomers mystified about their lack of jet signature.
Still, according to O’Connor, this finding “a massive step forward in our understanding of gamma-ray bursts,” the “equivalent Rosetta stone of long GRBs.”
O’Connor expects BOAT will yield more discoveries yet, as the afterglow is predicted to remain visible to scientists for at least another year.