On the morning of October 9, several space-based detectors caught a powerful gamma-ray burst (GRB) passing through our solar system, sending astronomers around the world rushing to train their telescopes on that part of the sky to collect vital data on the event and its subsequent glow. Nicknamed GRB 221009A, astronomers say the gamma-ray burst is the most powerful yet recorded, likely to be the “birth cry” of a new black hole. The event was immediately posted to Astronomer’s Telegram, and feedback is still ongoing.
“In our research group, we’ve been referring to this explosion as ‘BOAT,’ or the brightest of all time, because when you look at the thousands of explosions that gamma-ray telescopes have spotted since the 1990s, this telescope stands apart,” said Jillian Rastingad, a graduate student at the University of Northwestern Rastingad led one of two independent teams using the Gemini South telescope in Chile to study the event’s afterglow.
said Roberta Pellera, a graduate student at the Polytechnic University in Bari, Italy and a member of the Fermi Large Telescope (LAT) collaboration. “But it’s also among the most energetic and brightest of all, regardless of distance, which makes it doubly exciting.”
Gamma ray bursts are extremely high-energy explosions in distant galaxies lasting from milliseconds to several hours. The first gamma-ray bursts were observed in the late 1960s, thanks to the US launch of the Vela satellites. They were supposed to monitor the gamma ray signatures of nuclear weapons tests following the 1963 Nuclear Test Ban Treaty with the Soviet Union. The United States feared that the Soviets were conducting secret nuclear tests, in violation of the treaty. In July 1967, two of those satellites picked up a flash of gamma radiation that was clearly not a signature of a nuclear weapons test.
This data was kept away, but later Vela satellites with improved instruments recorded many gamma-ray bursts. A team at Los Alamos National Laboratory analyzed when each explosion was detected by different satellites to estimate the location of the sky for 16 such bursts. They determined that the bursts were not from Earth or our solar system, and published their conclusions in a research paper published in 1973 in the Astrophysical Journal.
There are two classes of gamma ray bursts. Most (70 percent) are long bursts lasting more than two seconds, often with a bright glow. These are usually associated with galaxies with rapidly forming stars. Astronomers believe that long eruptions are associated with the death of massive stars that collapse to form a neutron star or black hole (or, alternatively, a newly formed magnetar). The small black hole will produce jets of high-energy particles moving near the speed of light, powerful enough to penetrate the remnants of the progenitor star, and emit X-rays and gamma rays.
Gamma-ray bursts lasting less than two seconds (about 30 percent) are short bursts, usually emitted from regions of very little star formation. Astronomers believe that these gamma-ray bursts are the result of a merger of two neutron stars, or the merging of a neutron star with a black hole, forming a “kilonova”.
This hypothesis was confirmed in 2017, when the LIGO collaboration captured the gravitational wave signal of two merging neutron stars, accompanied by powerful gamma-ray bursts associated with kilonova. Earlier this year, astrophysicists spotted a mysterious X-ray that they believe could be the first detection of a kilonova’s “afterglow” from the merger itself. (Alternatively, it could be the first observation of matter falling into a black hole that formed after merging.)
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