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NASA’s Fermi gamma-ray space telescope has discovered a never-before-seen feature while studying what may be the most powerful explosion since the Big Bang. It could be the result of matter and antimatter particles annihilating at 99.9% of the speed of light.
The explosion was an example of a gamma-ray burst (GRB); it was first designated GRB 221009A when it was seen by NASA’s Fermi Gamma-ray Space Telescope and Neil Gehrels Swift Observatory on October 9, 2022. The GRB’s power quickly became apparent, earning it the nickname Brightest of All Time, or “BOAT”.
“As far as we can detect GRBs, there’s no doubt that this GRB is the brightest we’ve ever seen, by a factor of 10 or more,” explains Wen-fai Fong, an associate professor of physics and astronomy who is the leader of the Fong Group at Northwestern and one of BOAT’s discoverers, at the time it was thought to be this bright.
Scientists theorize that BOAT was launched by a supernova explosion that accompanied the death and collapse of a massive star about 2.4 million light-years away, possibly leaving behind a black hole.
Relating to: Scientists identify origin of ‘BOAT’, brightest cosmic explosion of all time
“A few minutes after BOAT exploded, Fermi’s Gamma-Ray Burst Monitor recorded an unusual energy peak that caught our attention,” study leader Maria Edvige Ravasio of Radboud University said in a statement. “When I first saw this signal, I got goosebumps. Our analysis since then shows that this is the first high-confidence emission line seen in the 50 years we have been studying GRBs.”
What did Fermi find in BOAT?
The first gamma-ray burst was seen by the US Vela satellites in 1967; it was officially documented two years later and made public in 1973.
Since then, scientists have detected numerous GRBs, and have determined that these brief flashes of light have cosmic origins and are the most powerful and violent explosions in the known universe. The most common type of GRB occurs when stars at least eight times the mass of the sun run out of fuel for nuclear fusion in their cores and can no longer resist the inward push of their own gravity; their cores collapse. This creates a spinning black hole that funnels matter to its poles and expels it as jets traveling at speeds close to the speed of light.
When these jets are directed directly at Earth, we see them as a GRB.
GRBs are so powerful that if they exploded within a few thousand light-years of Earth, they could destroy life on our planet by disrupting or destroying its atmosphere. But even among these terrifying events, BOAT stood out immediately.
Scientists eventually used statistics from other observed GRBs to determine that an event as powerful and bright as BOAT would only be visible in Earth’s sky once every 10,000 years. They also found that BOAT did indeed have an impact on Earth’s atmosphere, despite occurring 2.4 billion light-years away.
On October 9, 2022, high-energy gamma-ray light from BOAT saturated most of the orbiting gamma-ray detectors, including those at Fermi. This essentially prevented the burst’s true power from being measured at the peak of its duration. However, about five minutes after BOAT was detected, it dimmed enough to allow Fermi to see it again. The NASA gamma-ray telescope spotted an interesting feature in its light, or “spectrum,” called a “hypothetical emission line.”
When light passes through matter, elements absorb and emit light at specific frequencies, leaving “fingerprints” of absorption and emission in that light. This means scientists can reconstruct the elements the light passed through and determine the chemical composition of the objects it interacted with.
“While some previous studies have reported possible evidence for absorption and emission features in other GRBs, subsequent investigations have revealed that these could all be just statistical fluctuations. What we see in BOAT is different,” team member Om Sharan Salafia of the INAF-Brera Observatory in Milan said in the statement. “We determined that the probability of this feature being just a noise fluctuation is less than one in half a billion.”
The emission line that Fermi saw in the light from BOAT lasted about 40 seconds and reached a peak energy of 12 million electron volts (MeV). In the visible region of the electromagnetic spectrum, the energy of the light is between two and three electron volts (eV).
Researchers think they know what causes this feature. Every matter particle has a “twin” of antimatter particles. When these particles come together, they annihilate and release their energy back into the universe. It’s possible that the spectral feature the team saw in BOAT is caused by electrons and their antimatter counterparts, positrons, annihilating.
“When an electron and a positron collide, they annihilate, producing a pair of gamma rays with an energy of 0.511 MeV,” team member Gor Oganesyan of the Gran Sasso Institute of Science said in a statement. “Since we are looking at the jet, where matter is moving at close to the speed of light, this emission is heavily blue-shifted and pushed towards much higher energies.”
If the team is right, the particles would have been traveling at about 99.9% of the speed of light before they annihilated each other.
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“Despite decades of studying these incredible cosmic explosions, we still don’t understand the details of how these jets work,” said team member Elizabeth Hays, a Fermi project scientist at NASA’s Goddard Space Flight Center. “Finding clues like this is extraordinary.”
The team’s research was published in the journal Science on Friday (July 26).