Gamma-Ray Bursts (GRBs) were first discovered by satellites originally intended to scan for nuclear weapon detonations.They range from bursts of ten milliseconds to several hours, and also have differing energy levels. They are generally unexplained.

The near complete lack of observational constraint led to a profusion of theories, including evaporating black holes, magnetic flares on white dwarfs, accretion of matter onto neutron stars, antimatter accretion, supernovae, hypernovae, and rapid extraction of rotational energy from supermassive black holes, among others."

Source : Wikipedia

Note that the size of the highest energy bursts currently has no explanation of any kind. "No known process in the Universe can produce this much energy in such a short time."

Extremely high energy photons from the most powerful (scientifically recorded) GRB arrived near Earth on October 9, 2022. The burst, known as GRB 221009A, happened roughly 2 billion years ago. It was so powerful that most of the satellite-based gamma-ray detectors were temporarily 'blinded' by it. The energy released in a few hours (mainly X-rays and gamma rays*) was several orders of magnitude larger than the Sun will emit during its entire lifetime. As noted above, there is no known mechanism which could account for this. (ref.)

*Notes :

1) 'Gamma ray' is a slightly misleading but commonly-used term to describe extremely high energy (i.e. extremely high frequency) photons. They are more energetic than X-rays, and are defined as photons with frequencies above 30 exahertz ( 3×10¹⁹ Hz ).

2) A comprehensive list of observed GRBs from 28 February 1997 to 18 August 2023 can be found here courtesy Royal Astronomical Society, UK

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