The star that caused the brightest explosion ever recorded in the universe raises new questions for astrophysicists

This artist’s illustration published by the European Southern Observatory on January 6, 2014 shows supernova 1987A, based on real data with the cold interior regions of the exploded star’s remains.

This artist's illustration published by the European Southern Observatory on January 6, 2014 shows supernova 1987A, based on real data with the cold interior regions of the exploded star's remains.This artist's illustration published by the European Southern Observatory on January 6, 2014 shows supernova 1987A, based on real data with the cold interior regions of the exploded star's remains.

©AFP PHOTO / ESO / ALMA / NAOJ / NRAO / ALEXANDRA ANGELICH

Supernova

Atlantico: In 2022, an impressive ray of light was observed. This ray comes from the explosion of a supernova. If this type of explosion is known, why has this precise phenomenon so impressed the scientific community, in particular researchers from Northwestern University of Illinois and the University of Utah who have just published a new study?

Olivier Sanguy: This “ray of light” was noticed because of its intensity in gamma radiation. Observed in October 2022, the phenomenon lasted 7 minutes and was distinguished by an intensity 100 times greater than what had been measured previously. Gamma events of this type, linked to a supernova, are not exceptional. It is indeed the magnitude observed that is. Fortunately, the coordination of observatories at the international level made it possible to direct several telescopes, including the James Webb Space Telescope, towards the source concerned in order to accumulate the data.

In theory, this type of explosion helps create precious metals such as gold. But in this case these elements were not observed. How does this create a new mystery?

We must first remember that, during the Big Bang, the only atoms formed were the lightest, namely helium and deuterium (isotope of hydrogen) with a little lithium and beryllium. This is called primordial nucleosynthesis. The problem is that we are surrounded, and made up, of “heavier” elements like iron, oxygen or carbon. We know that they were forged thanks to nuclear reactions within the stars which dispersed them by exploding. Hence the exact expression that we are made of stardust. This is stellar nucleosynthesis. However, these two mechanisms do not explain all the elements. There is cosmic spallation (action of cosmic radiation which produces some elements such as boron) and especially explosive nucleosynthesis, which you mention in your question. The conditions specific to a supernova thus allow the creation of sulfur, potassium, chromium, cobalt or nickel. The list is not exhaustive. As for gold or other heavy metals such as platinum or uranium, we lean towards the end of the most extreme stars in order to provide the necessary conditions and not just the “common” supernova. The mystery for the October 2022 gamma-ray flash is that the affected star that exploded does not show traces of gold or other metals that we theoretically associate with such a strong event.

Another mystery remains, the explosion was not as powerful as imagined based on the gamma rays recorded. How does this challenge our understanding of astronomy?

In fact, astronomers consider that the power of gamma radiation (100 times above usual measurements, remember) is not necessarily linked to the importance of the supernova. First possibility, such a gamma flash could have had a source other than the supernova. This would therefore be banal and the absence of gold or other heavy metals unsurprising. An idea put forward by Peter Blanchard of Northwestern University in the United States. Another possibility, also explained by Tanmoy Laskar of the University of Utah in the United States, lies in the concentration of the jet of light in question. It is based on a comparison with a flashlight whose flow of light can be concentrated. If you point it straight into your eyes, the shine seems much stronger. Gamma-ray events like the one in October 2022 are associated with particle jets. If it were concentrated and directed towards the Earth, we understand its high magnitude without the need for an extreme supernova. The two scientists cited participated in the study of the October 2022 event. Their conclusion is that we must continue to observe supernovae in order to consolidate or possibly call into question the mechanisms and energy levels necessary for the creation of heavy metals.