In October 2022, space telescopes detected the most powerful gamma ray burst ever recorded. Known as GRB 221009A and dubbed the “BOAT” (Brightest Of All Time), this explosion was so intense it overwhelmed multiple instruments designed to study such events. Now, new observations from this burst are helping us to understand one of the universe’s most mysterious phenomena.
This sequence constructed from Fermi Large Area Telescope data reveals the sky in gamma rays centered on the location of GRB 221009A. (Credit : NASA/DOE/Fermi LAT Collaboration)
Gamma ray bursts are among the most powerful events in the universe, releasing more energy in seconds than our Sun will produce in its entire 10 billion year lifetime. These brilliant flashes occur when massive stars collapse into black holes or when neutron stars collide. The initial burst lasts only seconds to minutes, followed by an afterglow that gradually fades over hours to months.
Despite their incredible brightness, gamma ray bursts are notoriously difficult to study. They occur in distant galaxies billions of light years away, and their gamma rays weaken significantly during the long journey to Earth. Their brief, unpredictable nature makes catching them in the act extremely challenging.
Swift captured the afterglow of GRB 221009A about an hour after it was first detected. The bright rings form as a result of X-rays scattered from otherwise unobservable dust layers within our galaxy that lie in the direction of the burst. (Credit : NASA/Swift)
When GRB 221009A erupted, it triggered follow up observations worldwide. The ‘Large Sized Telescope’ (LST-1) in La Palma, Spain, began studying the burst just 1.33 days after the initial explosion. Over the following 20 days, researchers collected data that revealed something unexpected.
The team detected an excess of high energy gamma rays from the burst’s afterglow. While this signal wasn’t strong enough to claim a formal detection by scientific standards, it provided valuable clues about the burst’s structure and behaviour. The observations support a more complex picture of how gamma ray bursts work. It’s long been debated whether these explosions produce simple, uniform jets of plasma or more complicated structures. The LST-1 data suggests that GRB 221009A involved a structured jet, essentially a narrow, ultra fast core surrounded by a wider, slower moving shell of material.
The LST-1 pictured at the Observatorio del Roque de los Muchachos on the Canary island of La Palma.
This challenges the simpler ‘top-hat’ model that many researchers previously used to understand these events. The structured jet model helps explain how particles get accelerated to extreme energies and why we see the specific patterns of radiation that we do.
The LST-1 telescope achieved something remarkable during these observations. It successfully collected data under very bright moonlight conditions, a significant challenge given its extremely sensitive cameras. The full Moon initially prevented other similar telescopes from observing the burst, but technical innovations by the LST team allowed them to continue working despite the bright conditions.
Their new observational technique now opens new possibilities for studying transient events, even when lunar conditions would normally make observations impossible. The success with GRB 221009A marks just the beginning of a new era in high energy astrophysics, where researchers can examine the inner workings of astronomical sources in extraordinary detail.
Source : Brightest gamma-ray burst hints at hidden layers in cosmic jet formation