Scientists unravel massive star as reason behind brightest of all time explosion

By Arya M Nair, Official Reporter
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GRB 221009A explosion
Rep.Image | NASA

Scientists have discovered the brightest gamma-ray burst (GRB) to date, GRB 221009A, which presented an opportunity to spectroscopically test the idea that rapid neutron-capture process (r-process) elements are produced following the collapse of rapidly rotating massive stars.

The study presents James Webb Space Telescope observations of GRB 221009A obtained +168 and +170 rest-frame days after the gamma-ray trigger, and demonstrated that they are well described by an SN 1998bw-like supernova (SN) and power-law afterglow, with no evidence for a component from r-process emission.

The explosion was detected by telescopes in October 2022. It came from a distant galaxy 2.4 billion light-years away, emitting light across all frequencies. But it was especially intense in its gamma rays, which are a more penetrating form of X-rays.

The B.O.A.T

GRB 221009A, a long gamma-ray burst, was so bright it effectively blinded most gamma-ray instruments in space. Subsequent readings showed that the burst was 100 times brighter than anything that had ever been recorded before, earning it the nickname among astronomers of the Brightest Of All Time or B.O.A.T.

The SN is only slightly fainter than the brightness of SN 1998bw at this phase, which indicates that the SN is not an unusual GRB-SN. This demonstrates that the GRB and SN mechanisms are decoupled and that highly energetic GRBs are not likely to produce significant quantities of r-process material, which leaves open the question of whether explosions of massive stars are key sources of r-process elements.

Moreover, the host galaxy of GRB 221009A has a very low metallicity and strong H2 emission at the explosion site, which is consistent with recent star formation, hinting that environmental factors are responsible for its extreme energetics.

Similar to other gamma-ray bursts, GRB 221009A had a jet that erupted from the collapsing star like it was shot into space from a fire hose, with gamma rays radiating from the hot gas and particles at the jet’s core.

Some of the most energetic gamma-ray jets have shown similar properties, but the jet from the BOAT was unique in one important way: The energy of the material in GRB 221009A also varied, meaning that instead of all the material in the jet having the same energy, like a single bullet shot from a gun, the energy of the of the material changed with distance from the jet’s core. This has never been observed in a long gamma-ray burst jet before.

Prof Catherine Heymans of Edinburgh University and Scotland’s Astronomer Royal, who is independent of the research team, said that, “The results like these help to drive science forward. The Universe is an amazing, wonderful and surprising place, and I love the way that it throws these conundrums at us. The fact that it is not giving us the answers we want is great, because we can go back to the drawing board and think again and come up with better theories.”

Where the heavy elements go?

One theory is that one of the ways heavy elements, such as gold, platinum, lead and uranium, might be produced during the extreme conditions that are created during supernovas, are spread across the galaxy and are used in the formation of planets, which is how, the theory goes, the metals found on Earth arose.

There is evidence that heavy elements can be produced when dead stars, called neutron stars collide, a process called a kilonovae, but it’s thought that not enough could be created this way. The team will investigate other supernova remnants to see if heavy elements still can be produced by exploding stars but only under specific conditions.

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