Scientists find evidence of extremely heavy elements in ancient stars

Scientists believe that many of the elements found in the Universe that are heavier than iron are created when stars merge or explosively die, but they are still unsure about the cosmic origin of several elements and the full array of processes that form heavy elements.. The source of naturally-formed elements heavier than uranium is especially unclear, and no one has directly detected such elements in space.

Now, by analyzing the chemical composition of 42 ancient stars in the Milky Way, researchers show that the stars produced elements with atomic masses larger than 260, heavier than any element found naturally on Earth (Science 2023, DOI: 10.1126/science.adf1341) . Fission of these radioactive nuclei is a major cosmic source of elements heavier than iron, they suggest.

Scientists look at light spectra from stars to identify the proportions of various elements inside. Studies so far have focused on the detailed elemental composition of one star or compared relative amounts of a few elements in several stars, says Ian Roederer, a physicist and astronomer at North Carolina State University.

To reveal a more complete picture, he and his colleagues analyzed the element patterns of “every star we could find in published literature with high levels of heavy elements,” he says. Specifically, they looked at elements from selenium to platinum, atomic numbers 34 to 78. They found a direct correlation between the amounts of elements with atomic numbers 44 to 47 (ruthenium to silver), and of slightly heavier ones with atomic numbers 63 to 78 (europium to platinum). There was no similar behavior among elements adjacent to the two groups.

The only reasonable explanation is that the correlated elements came from a common source, he says. Adding the atomic mass numbers of the two element sets indicates that the stars had produced elements with atomic mass over 260, and these radioactive transuranic nuclei split into two fragments, a smaller one with lighter elements from the silver to ruthenium group and a larger one with the slightly heavier element group.

Darach Jafar Watson, an astrophysicist at the University of Copenhagen, says “the correlation stands out strongly. I cannot think of an alternate explanation, and while it is not conclusive, it seems a likely and reasonable interpretation.”