Every now and again, the night sky lights up with spectacular explosions blazes with the most energetic light our Universe can produce. Known as gamma-ray bursts, they can release in seconds what our Sun will emit in its lifetime.
Now scientists have discovered a never-before-seen signal buried in the spectrum of electromagnetic radiation sent by the brightest gamma rays ever recorded.
The signal is emission light – bright regions in the gamma ray spectrum produced by objects that emit light at a certain wavelength. And something, scientists have determined, is complete and pronounced destruction: destroy together from electron-positron pair, matter and antimatter its pair.
Named ‘BOAT’ (short for Brightest Of All Time), the explosion was detected in October 2022. It is the result of a massive star exploding as its core collapses into a black hole, destroying many energetic photons. it has been difficult to take accurate measurements.
But the measurements were, indeed, taken, and the scientists knew from the beginning that they were looking at something special.
“A few minutes after BOAT exploded, Fermi’s Gamma-ray Burst Monitor recorded an unusual energy peak that caught our attention,” said astrophysicist Maria Edvige Ravasio of Radboud University in the Netherlands.
“When I first saw the signal, I got goosebumps. Our analysis since then has shown it to be the first high-confidence emission line ever seen in 50 years of studying gamma-ray bursts.”
Appearing as bright lines in the spectrum of light emitted from a source, emission lines indicate something that causes light of a certain wavelength to be brighter – an extra emission source. Additionally, darker lines known as absorption lines can appear where wavelengths of light are absorbed.
Emission and absorption features can tell us about the constituent chemistry of a wide range of astrophysical processes, from the metallicity of stars to the molecules in the atmospheric makeup of distant planets.
There are many different scenarios that can produce gamma-ray bursts, the most energetic bursts of light in the electromagnetic spectrum, but the one that produced BOAT – officially named GRB 221009A – is the birth of a black hole. The outer material of the star is thrown violently into space, while the core collapses under gravity to form the densest objects in the Universe.
This explosion is accompanied by jets or particles blasting out in the opposite direction. This is what we see in gamma-ray bursts, with jets tilted toward our line of sight.
When GRB 221009A first erupted, it was so bright that it obscured any details. Over 80 seconds, the explosion evolved from a peak energy of 12 million electron volts down to about 6 million electron volts. Just five minutes later, it had dimmed enough for the Fermi gamma-ray telescope to detect emission lines that lasted for at least 40 seconds.
Researchers believe that a phenomenon called annihilation is responsible for the better light. When an electron and its antimatter pair, a positron, collide, it produces a photon with an energy of 0.511 million electron volts.
The emission features observed in BOAT reflect higher energies, but the researchers have an explanation for this. The annihilation occurs in jets that approach us at about 99.9 percent of the speed of light. This makes the energy appear higher than it is, an illusion based on our vantage point that we can see in other astrophysical jets.
“Because we’re looking for jets, where matter is moving fast, this emission is very blue and pushed to higher energies,” explained astrophysicist Gor Oganesyan from the Gran Sasso Institute of Science in Italy.
Although it seems that GRB 221009A is an extreme example of a gamma-ray burst, subsequent observations and analyzes have revealed that BOAT is actually normal – its brightness is simply the result of orientation, exploding in our direction.
This is actually good news. That means we can use BOAT to understand how gamma ray bursts usually develop over time, and the processes that occur in them.
“After decades of studying these incredible cosmic explosions, we still don’t know the details of how these jets work,” said astrophysicist Elizabeth Hays of NASA’s Goddard Space Flight Center.
“Finding clues like these extraordinary emission lines will help scientists probe this extreme environment more deeply.”
The findings have been published in science.
