Stars at the dawn of time must have been capable of creating elements much heavier than anything found on Earth, or indeed in the wider universe.
This was the conclusion reached by a team of astronomers from the University of Michigan, led by Ian Roederer. Science Alert. They examined 42 stars in the Milky Way, whose chemical abundance can only be explained by the early formation of elements with atomic masses greater than 260.
Most of the elements in the universe, those heavier than hydrogen, were formed by stars. The first form of formation is fusion. In the core of stars, atoms are “blended together” and heavier elements are created.
The heaviest element this process can produce is iron. The fusion of iron into heavier elements requires much more energy than it produces, which is why the star is destroyed in this case.
However, there is another method based on self-destruction. In supernova and kilonova explosions, when two neutron stars collide, conditions become just right for the fast neutron capture process, i.e. the r process.
The universe may contain heavier elements than we have ever seen before
In this case, there are so many neutrons around that they collide with the available nuclei and form a heavier element. This requires a very energetic environment, such as a supernova.
In addition, the whole process happens very quickly. Elements such as gold, platinum, thorium and uranium have been confirmed to be produced in this process. But there is still a lot we don’t know about how elements are formed.
“We have a general idea of how the r process works, but the process conditions are very extreme,” Roederer explains.
We don’t know how many different types of places in the universe can create an r-process, we don’t know how an r-process ends, and we can’t answer questions like how many neutrons can be added.
“Or how heavy the element is at all. So we decided to look at some already known stars for elements that could fission to see if we could answer some of these kinds of questions.”
The other way we know that elements can be created is through nuclear fission. In this case, the atom splits rather than fuses, and the result is an element with a lower mass.
The chemical composition of the 42 stars in the Milky Way that Roeder and his team studied is already well studied.
The first stars in the universe were composed mostly of hydrogen. These stars formed the elements in their cores and then died, flooding the space around them with elements that were picked up by subsequent generations of stars.
In the case of the stars examined by the research group, it is known that the elements were formed during supernova explosions during the r process.
However, researchers have not looked for elements of the r process. They looked for elements that could be fission products, such as ruthenium, rhodium, palladium and silver. Instead of studying the stars individually, as they usually do, the researchers studied them as a group.
Hot on the trail
Thanks to this, a pattern was found. Certain other elements in certain frequency ratios would be expected if the minerals the team studied were formed during the r process. These percentages did not exist. According to this, the elements in question were formed by fission.
This means that the early stars from which these metals emerged could have produced elements much heavier than atomic mass 260, which later split into lighter, more stable elements.
We have never observed the natural occurrence of these elements anywhere. We’ve seen it in the lab, but its half-life is so short that it degrades almost instantly.
But the research shows that searching for potential fission products can tell us how likely or common their formation is in the wider universe.
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