Conceptual Imagery Lab at NASA’s Goddard Space Flight Center
Scientists have been in a panic ever since several space detectors picked up a powerful gamma-ray burst (GRB) in October 2022 — an explosion so energetic that astronomers nicknamed it BOAT (Brightest Outburst Ever). Now an international team of astronomers has analyzed an unusual energy peak detected by NASA’s Fermi Gamma-ray Space Telescope and concluded that it was an emission spectrum, according to New paper These results were published in the journal Science. According to the authors, it is the first high-confidence emission line ever observed in 50 years of studying gamma-ray bursts.
As previously mentioned, gamma-ray bursts are extremely high-energy explosions in distant galaxies lasting from just a millisecond to several hours. There are two classes of gamma-ray bursts. Most (70%) are long bursts lasting more than two seconds, often accompanied by a bright flare. These are typically associated with galaxies with rapid star formation. Astronomers believe that long bursts are associated with the death of massive stars that collapse to form a neutron star or black hole (or, alternatively, a newly formed magnetar). A small black hole would produce jets of high-energy particles moving at close to the speed of light, powerful enough to penetrate the remains of the progenitor star, and emitting X-rays and gamma rays.
Gamma-ray bursts lasting less than two seconds (about 30 percent) are short bursts, and are usually emitted from regions with very little star formation. Astronomers believe that these gamma-ray bursts are the result of the merger of two neutron stars, or the merger of a neutron star with a black hole, forming a “kilonova.” This hypothesis has been put forward Confirmed in 2017 When the LIGO collaboration picked up the gravitational wave signal of two neutron stars as they merged, accompanied by powerful gamma-ray bursts associated with kilonovae.
Several papers It was published. Last year, NASA published a report on the analysis of all the observational data. These results confirmed that gamma-ray burst 221009A was indeed a BOAT, appearing particularly bright because its narrow jet was pointing directly at Earth. But the various analyses also yielded several surprising results that puzzled astronomers. Most notably, a supernova was supposed to have occurred a few weeks after the initial explosion, but astronomers didn’t detect one, perhaps because it was so faint, and thick clouds of dust in that part of the sky were blocking out any incoming light.
Earlier this year, astronomers confirmed that the boat came from a supernova, thanks to signs of basic elements like calcium and oxygen that we would expect to find in a supernova. However, they found no evidence of expected heavy elements like platinum and gold, which ties into the long-standing question of where such elements originated in the universe. The boat may be special in this regard; more data will tell us more.
“gave me goosebumps”
Just minutes after the eruption, Fermi’s gamma-ray burst monitor recorded an unusual energy peak. Scientists now say the feature is the first high-confidence emission line ever observed in 50 years of studying gamma-ray bursts.
According to the authors, the newly discovered spectral emission line is likely the result of a matter-antimatter collision, producing a pair of gamma rays that are blue-shifted toward higher energies as we look into the jet. The presence of spectral emission associated with a GRB is important because it can shed light on the specific chemicals involved in the reactions. Previous studies have reported possible evidence of absorption or emission lines in other GRBs, but these have typically been shown to be likely statistical noise.
But that’s not the case with this latest discovery, according to co-author Om Sharan Salavia at the INAF-Brera Observatory in Milan, Italy, who He added that “The chances that this turns out to be a statistical fluctuation are less than one chance in half a billion,” says his colleague at the National Institute of Astrophysics and co-author, Maria Edwige Ravasio. He said that When she first saw the sign, “I got goosebumps.”
Why did it take astronomers so long to spot it? When BOAT first erupted in 2022, it saturated most of the gamma-ray detectors in space, including the Fermi Space Telescope, leaving them unable to measure the most intense part of the burst. The emission line didn’t appear until a good five minutes after the burst, when it had dimmed enough for Fermi to make a measurement. The spectral emission lasted for about 40 seconds and reached a peak energy of about 12 MeV, compared to 2 or 3 MeV for visible light, according to the authors.
Science, 2024. DOI: 10.1126/science.adj3638 (About DOIs).
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