Ancient stars can produce elements with more than 260 protons

R-process nucleosynthesis. Source: Lawrence Livermore National Laboratory

The first stars in the universe were monsters. Consisting only of hydrogen and helium, it would be 300 times more massive than the sun. Inside them, the first of the heavier elements are formed, then thrown into the universe at the end of their short lives. They are the seeds of all the stars and planets we see today. A new study published in Science suggesting that these ancient ancestors created more than natural elements.

Except for hydrogen, helium, and some traces of other light elements, all the atoms we see around us are created by astrophysical processes, such as supernovae, collisions of neutron stars, and high -energy particle collisions. Together they create heavier elements up to Uranium-238, which is the heaviest naturally occurring element. Uranium is formed in supernova and neutron star collisions through the so-called r-process, where neutrons are rapidly captured by atomic nuclei to form a heavier element. The r-process is complex, and we still don’t understand much about how it happens, or what its upper mass limit is. This new study, however, suggests that the r-process in the earliest stars may have produced heavier elements with atomic masses greater than 260.

The team looked at 42 stars in the Milky Way where the elemental composition is best understood. Instead of just looking for the presence of heavier elements, they looked at the relative abundance of the elements in all the stars. They found that the abundance of some elements such as silver and rhodium did not agree with the predicted abundance from the known r-process nucleosynthesis. The data suggest that these elements are the decay remnants from heavier nuclei greater than 260 atomic mass units.

In addition to the r-process of fast neutron capture, there are two other ways to create heavy atomic nuclei: the p-process in which neutron-rich nuclei capture protons, and the s-process in which the a seed nucleus captures a neutron. But none of these can produce a rapid mass build-up required for elements beyond uranium. And it is only in hypermassive first-generation stars that the r-process nucleosynthesis can create such elements.

Therefore, the study suggests that the r-process can create elements beyond uranium, and probably did so within the early stars of the universe. Unless there is an island of stability for some of these ultra-heavy elements, they will long ago decay into the natural elements we see today. But the fact that they once existed helps scientists better understand the r-process and its limitations.

More information:
Ian U. Roederer et al, Element abundance patterns in stars indicate fission of nuclei heavier than uranium, Science (2023). DOI: 10.1126/science.adf1341. on arXiv: DOI: 10.48550/arxiv.2312.06844

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Citation: Ancient stars can produce elements with more than 260 protons (2023, December 23) retrieved on December 23, 2023 from https://phys.org/news/2023-12-ancient-stars-elements -protons.html

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