Ceci n'est pas un caillou, mais le reliquat d'une rare supernova

Ceci n’est pas un caillou, mais le reliquat d’une rare supernova

A stone discovered in Egypt in 1996 seems to have come from a thermonuclear supernova that took place light years away from us, several billion years ago. How have scientists traced the dizzying history of this stone?

It weighs 33 grams and is called Hypatia. It’s a stone. But it is quite different from the ones you can usually pick up, because it comes from afar. Discovered in 1996 in Egypt, Hypatia is an extraterrestrial stone (literally). It most likely comes from the nucleus of a comet. Because of this specificity, it is studied thoroughly.

A study, which will be published in August 2022 in the scientific journal Icarus (but already available), suggests that Hypatia is even more fascinating: it would be the remnant of a supernova, and, in addition, of a rare type of which we had no material trace for the moment on Earth. How can we trace the potential interstellar history of a pebble?

Fragments of Hypatia (with a coin at the bottom). // Source: University of Johannesburg

Here is the (potential) history of Hypatia

The chemical composition of any object tells a story. It reveals a chronology and a provenance. That of Hypatia suggests that it comes from dust and particularly characteristic gases: it would come from a “parent” object which would have itself formed from a type Ia supernova, that is to say say thermonuclear. The shape of the rock, that is to say the way in which all this material has aggregated, constitutes an additional clue.

In a way, we can say that we surprised the explosion of a supernova Ia in full action, because the gas atoms from this explosion were caught in the surrounding dust cloud, which eventually formed the parent body of Hypatia “, Details one of the authors, Jan Kramers, on the site of the University of Johannesburg on May 17.

The dating is just as dizzying, since it would mean that the stone was formed over the last billion years, when our solar system was just born (some 4 billion years ago).

Thermonuclear supernova or not: what is the level of certainty?

To reach this conclusion, the scientists carried out a chemical analysis by targeting 17 areas of a very small sample of Hypatia. The result showed that there were low levels of silicon, chromium and manganese. This first observation ensures that the stone does not come from the solar system. Then, the analysis showed that, on the other hand, there were high levels of iron, sulphur, phosphorus, copper and vanadium: this second observation shows that the object does not come from the spatial vicinity, nor even from our arm of the Milky Way.

The composition also rules out a red giant star as a source. Similarly, the chemical analysis shows that Hypatia contains too high a rate of iron compared to silicon and calcium, which excludes the origin of a type Ib supernova (known as ” at heart collapse “).

By proceeding in this way by successive exclusions, only one possibility remained, and the most intriguing of all: the thermonuclear supernova Ia. These supernovae from binary stars are rare, but it is speculated that any resulting rock must contain certain chemical elements in unusual proportions. However, precisely, all the analyzes of Hypatia make it possible to “match” the stone with what is expected of a thermonuclear supernova.

Well almost. Scientists have also identified chemical elements (such as phosphorus or potassium) that do not seem compatible with this type of supernova. However, this is not inexplicable: these elements can be derived from various events that took place in the region, before or during the supernova. In summary, at this stage of research, we can consider Hypatia as the most probable material trace – found on Earth – of a supernova Ia. And that’s already not bad as proof, since we are talking about a gigantic explosion that took place billions of years ago, several light years away.

Look at the world from space

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