Combined HST images WFC3/UVIS and WFC3/IR (F625W, F125W, F160W) of the GRB 221009A field, observed on 2022 December 4. Note the clear appearance of an underlying host galaxy, with a disklike morphology. GRB 221009A is slightly offset from the center of the apparent host, off the disk plane. Credit: The Astrophysical Journal Letters (2023). DOI: 10.3847/2041-8213/acbd50
University of Arizona astronomers have joined an international effort to study the aftermath of the brightest flash of gamma rays ever observed. Observations involving various UArizona telescopes and instruments provide astronomers with a "cosmic lab" to study how massive stars die.
On Oct. 9, a pulse of intense radiation swept through the solar system, so exceptional that astronomers quickly dubbed it the BOAT—the brightest of all time. The source was a gamma-ray burst, or GRB—the most powerful class of explosions in the universe.
The burst triggered detectors on numerous spacecraft, and observatories around the globe followed up. After combing through all of the data, astronomers can now characterize just how bright it was and better understand its scientific impact. Two research teams at the University of Arizona joined the international effort to obtain and analyze the data to better understand what causes these outbursts of cosmic proportions. Papers describing the results will appear in a focus issue of The Astrophysical Journal Letters.
"This flash of gamma rays was the brightest burst ever recorded," said Kate Alexander, an assistant professor in the UArizona Department of Astronomy and Steward Observatory, who co-authored one of the papers. "You would expect one of this magnitude about once in 10,000 years."
Observations of the burst span the electromagnetic spectrum, from radio waves to gamma rays, and include data from many NASA and partner missions, including the National Science Foundation's Karl G. Jansky Very Large Array radio telescope in New Mexico, NASA's NuSTAR observatory and even Voyager 1 in interstellar space. Alexander and other scientists presented new findings about the BOAT at the High Energy Astrophysics Division meeting of the American Astronomical Society in Waikoloa, Hawaii, on Tuesday.
The signal from the gamma ray burst, dubbed GRB 221009A, had been traveling for about 1.9 billion years before it reached Earth, making it among the closest known "long" GRBs, whose initial, or prompt, emission lasts more than two seconds. Astronomers think these bursts represent the birth cry of a black hole that formed when the core of a massive star collapsed under its own weight. As it quickly ingests the surrounding matter, the black hole blasts out jets in opposite directions containing particles accelerated to near the speed of light. These jets pierce through the star, emitting X-rays and gamma rays as they stream into space. As these streams of matter expand out into space, they crash into gas and dust around the star, producing long-lasting "afterglow" light that telescopes can detect across the entire electromagnetic spectrum.
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