An article published in the journal “Nature Astronomy” reports a study on the gamma-ray burst cataloged as GRB221009A, the brightest ever detected, which confirms that it was caused by the collapse of a massive star, which subsequently exploded in a supernova. A team of researchers led by Northwestern University used data collected with the James Webb Space Telescope and the ALMA radio telescope to obtain the information needed to support their conclusions. The mystery remains of the absence of traces of the generation of heavy elements such as platinum and gold, which they thought could be associated with supernovae that lead to very powerful gamma-ray bursts.
The GRB221009A gamma-ray burst was observed on October 9, 2022, and from the beginning, astronomers realized its extreme power. It was called the gamma-ray burst of the century and the Anglo-Saxon media also called it the BOAT, an acronym that means Brightest Of All Time.
The first analyzes of the GRB221009A gamma-ray burst were published just over a year ago with reconstructions in which there was the collapse of the core of a massive star which led to the birth of a black hole that emits relativistic jets of very high energy particles in opposite directions as it swallows the materials around it.
The study of the GRB221009A gamma-ray burst continued and now the team from Northwestern University brought confirmation of the previous reconstruction with some surprises. The researchers used observations conducted by the James Webb Space Telescope’s NIRSpec and MIRI instruments to obtain near-infrared spectroscopic data of the event and its aftermath.
The residual glow, called afterglow in jargon, offers information but at the same time hides the traces of the supernova, so it was necessary to wait months for the brightness to fade away enough. To separate the supernova light from the afterglow, the researchers combined the observations conducted with Webb with others conducted with the ALMA radio telescope.
When the researchers were able to obtain the data they were looking for, they saw that the supernova that generated the GRB221009A gamma-ray burst appeared normal, similar to others that generated far less powerful gamma-ray bursts. In the generation of chemical elements, the supernova seems normal as well: spectroscopic traces of elements such as calcium and oxygen were detected but not of heavier ones such as gold and platinum.
One hypothesis regarding the power of the GRB221009A gamma-ray burst links it to the shape and structure of the relativistic jets emitted by the newborn black hole. If these jets are narrow, they produce a more concentrated and brighter beam of light. Supporting this hypothesis is one of the narrowest jets seen so far during a gamma-ray burst.
Studies of the GRB221009A gamma-ray burst are far from over and may include examinations of the surrounding environment. Spectroscopic observations of the galaxy hosting the progenitor star show traces of intense star formation. The environment in which that star was born could be peculiar in terms of its chemical characteristics, with a lower presence than the average of elements heavier than hydrogen and helium. In short, an almost primordial gas, very little enriched by heavy elements generated by previous supernovae.
Understanding whether the characteristics of the host galaxy influenced the power of the GRB221009A gamma-ray burst is one of the next steps of the research. At the beginning of the studies someone thought they could find explanations for its power not predicted by current models but now that seems less likely. The interest in an extraordinary event remains alive and the considerable amount of detections, which continued over time to monitor its evolution, help to carry out in-depth analyses.
