The brightest gamma-ray burst ever recorded recently lit up a distant galaxy — and astronomers have nicknamed it the BOAT, for Brightest of All Time.
“We use the boat emoji a lot when we’re talking about it” on the messaging app Slack, says astronomer Jillian Rastinejad of Northwestern University in Evanston, Ill.
Gamma-ray bursts are energetic explosions that go off when a massive star dies and leaves behind a black hole or neutron star (SN: 11/20/19; SN: 8/2/21). The collapse sets off jets of gamma rays zipping away from the poles of the former star. If those jets happen to be pointed right at Earth, astronomers can see them as a gamma-ray burst.
This new burst, officially named GRB 221009A, was probably triggered by a supernova giving birth to a black hole in a galaxy about 2 billion light-years from Earth, researchers announced October 13. Astronomers think it released as much energy as roughly three suns converting all of their mass to pure energy.
NASA’s Neil Gehrels Swift Observatory, a gamma-ray telescope in space, automatically detected the blast October 9 around 10:15 a.m. EDT, and promptly alerted astronomers that something strange was happening.
“At the time, when it went off, it looked kind of weird to us,” says Penn State astrophysicist Jamie Kennea, who is the head of science operations for Swift. The blast’s position in the sky seemed to line up with the plane of the Milky Way. So at first Kennea and colleagues thought it was within our own galaxy, and so unlikely to be something as dramatically energetic as a gamma-ray burst. If a burst like this went off inside the Milky Way, it would be visible to the naked eye, which wasn’t the case.
But soon Kennea learned that NASA’s Fermi Gamma-ray Space Telescope had also seen the flash — and it was one of the brightest things the telescope had ever seen. A fresh look at the Swift data convinced Kennea and colleagues that the flash was the brightest gamma-ray burst seen in the 50 years of observing these rare explosions.
“It’s quite exceptional,” Kennea says. “It stands head and shoulders above the rest.”
After confirmation of the burst’s BOAT bonafides — a term coined by Rastinejad’s adviser, Northwestern astronomer Wen-fai Fong — other astronomers rushed to get a look. Within days, scientists around the world got a glimpse of the blast with telescopes in space and on the ground, in nearly every type of light. Even some radio telescopes typically used as lightning detectors saw a sudden disturbance associated with GRB 221009A, suggesting that the burst stripped electrons from atoms in Earth’s atmosphere.
In the hours and days after the initial explosion, the burst subsided and gave way to a still relatively bright afterglow. Eventually, astronomers expect to see it fade even more, replaced by glowing ripples of material in the supernova remnant.
The extreme brightness was probably at least partially due to GRB 221009A’s relative proximity, Kennea says. A couple billion light-years might seem far, but the average gamma-ray burst is more like 10 billion light-years away. It probably was also just intrinsically bright, though there hasn’t been time to figure out why.
Studying the blast as it changes is “probably going to challenge some of our assumptions of how gamma-ray bursts work,” Kennea says. “I think people who are gamma-ray burst theorists are going to be inundated with so much data that this is going to change theories that they thought were pretty solid.”
GRB 221009A will move behind the sun from Earth’s perspective starting in late November, shielding it temporarily from view. But because its glow is still so bright now, astronomers are hopeful that they’ll still be able to see it when it becomes visible again in February.
“I’m so excited for a few months from now when we have all the beautiful data,” Rastinejad says.