What is GRB 221009A?

April 1, 2023

In October 2022, astronomers recorded a pulse of gamma-ray radiation that could potentially overturn a decades-long theory of gamma-ray burst (GRB) jets. The radiation was captured by a joint observation involving several institutions, including the Center for Astrophysics, Harvard and Smithsonian’s Submillimeter Array (SMA) in Hawaii, the Atacama Large Millimeter Array (ALMA) in Chile, the MeerKAT Array in South Africa, the US National Science Foundation’s Karl G Jansky Very Large Array (VLA) in New Mexico (USA), and NCRA’s Giant Metrewave Radio Telescope in India. The name given to this observation was GRB 221009A.

Gamma-Ray Radiation and Black Holes

Long-duration GRBs are the consequence of the birth of a black hole, which is formed when the core of a massive star falls under its weight. The plasma jets formed by the formation of a new black hole release powerful gamma rays, and as these jets slam into the gas neighboring the dying star, a bright afterglow is produced across the spectrum.

Birth Cry of a Black Hole

When the astronomers analyzed the signals from the radiation pulse, they concluded that they were a birth cry of a black hole. However, the radio signals from the afterglow were brighter than expected, and the astronomers initially thought that they might have captured the fleeting signature of a ‘reverse shock.’

Challenging Decades-Old Theory on GRB Jets

The radio spectrum of GRB 221009A faded much too slowly to be a reverse shock. The outflow may consist of a small mass shooting at 99.4 per cent at the speed of light, and there is the possibility of a very fast-moving jet producing the X-ray and visible light in the afterglow. These findings challenge the decades-old theory on GRB jets, indicating the existence of a very fast-moving jet that produces the X-ray and visible light in the afterglow.

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