Astronomers captivated by the most luminous gamma-ray burst ever detected, believed to be a black hole's birth cry, uncover new cosmic explosion enigmas.
Unprecedented Gamma-Ray Burst Event
On October 9, 2022, a powerful gamma-ray pulse surged through our solar system, overwhelming gamma-ray detectors on various orbiting satellites and prompting astronomers to employ the world’s most potent telescopes to investigate the event. The newly discovered source, designated GRB 221009A, is the most brilliant gamma-ray burst (GRB) ever documented.
In a study published in The Astrophysical Journal Letters, observations of GRB 221009A across the radio to gamma-ray spectrum reveal crucial insights into the origins of these intense cosmic explosions, a decades-long pursuit for astronomers.
Birth Cry of a Black Hole
GRB 221009A’s gamma-ray emission persisted for over 300 seconds. Long-duration GRBs like this are thought to signal the formation of a black hole as a massive, rapidly spinning star’s core collapses under its weight. The nascent black hole produces near-light-speed plasma jets that penetrate the collapsing star and emit gamma-rays.
Unraveling Afterglow Mysteries
The real conundrum with GRB 221009A, the brightest burst ever recorded, lay in what would follow the initial gamma-ray surge. As the jets collide with surrounding gas, they create a rapidly fading, all-spectrum “afterglow” of light, explains the study’s lead author, Tanmoy Laskar. The SMA, operated by the Center for Astrophysics | Harvard & Smithsonian, was employed by astronomers to capture the afterglow before it vanished.
The resulting data was perplexing, as millimeter and radio wave measurements were much brighter than anticipated based on visible and X-ray light. A unique mechanism is likely behind the production of excess millimeter and radio waves, according to CfA researcher Yvette Cendes. The powerful jet produced by GRB 221009A may be more intricate than most GRBs, with visible and X-ray light emitted by one part of the jet and early millimeter and radio waves by another.
Continued Exploration of the Cosmic Enigma
The afterglow is so intense that astronomers will study its radio emission for months, possibly years, to determine the excess emission’s mysterious origin. Rapid response to GRBs and similar events using millimeter-wave telescopes, such as the SMA, is a critical new capability for astronomers, as it allows for potential discoveries about the most extreme explosions in the universe.
“This burst, being so bright, provided a unique opportunity to explore the detailed behavior and evolution of an afterglow with unprecedented detail — we did not want to miss it!” says Edo Berger, professor of astronomy at Harvard University and the CfA. “I have been studying these events for more than twenty years, and this one was as exciting as the first GRB I ever observed.”
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