Scientists have uncovered hints of a world of new elements beyond the periodic table. A new study has found that ancient stars may have been producing extremely heavy elements that remain unknown to science.
We owe the rich diversity of elements in the universe today to stars. These cosmic factories take elements from their environment and fuse them together to produce new ones, and when the stars eventually die they spread the fruits of their labor throughout the universe. That provides the next generation of stars with a more advanced slate to start with, allowing them to produce ever-heavier elements.
But what’s the limit to this process, and how heavy can an element get? Those questions were the focus of a new study by scientists at North Carolina State University.
Elements are said to be heavier or lighter depending on their atomic mass, which is defined as the number of protons and neutrons in the nucleus of a single atom of that element. The heaviest element that’s naturally occurring in meaningful quantities is uranium, with an atomic mass of 238 u. But the new study found evidence written in the stars of mysterious elements with atomic masses of over 260 u.
The heaviest elements are produced through what’s called the r-process, which can only take place in the extreme environments of neutron stars. Essentially, an atomic nucleus floating around in the star becomes flooded with neutrons in fractions of a second, before some of those neutrons are converted to protons. That results in an atom of a heavy element like platinum or uranium.
“The r-process is necessary if you want to make elements that are heavier than, say, lead and bismuth,” said Ian Roederer, lead author of the study. “You have to add many neutrons very quickly, but the catch is that you need a lot of energy and a lot of neutrons to do so. And the best place to find both are at the birth or death of a neutron star, or when neutron stars collide and produce the raw ingredients for the process.”
The team examined the composition of 42 well-studied stars in the Milky Way that are known to contain heavy elements forged in earlier generations of stars. Rather than looking at each star individually, the researchers studied the abundances of elements collectively across the group, and spotted patterns that had previously been missed.
Certain elements, including ruthenium, rhodium, palladium and silver, were found to be abundant in these stars, but elements right next to them on the periodic table didn’t have these same correlations. This, the team says, is evidence that these elements were formed by much heavier elements decaying. Working backwards, the researchers calculated that the starting heavy elements would have had atomic masses of at least 260 u.
“That 260 is interesting because we haven’t previously detected anything that heavy in space or naturally on Earth, even in nuclear weapon tests,” said Roederer. “But seeing them in space gives us guidance for how to think about models and fission – and could give us insight into how the rich diversity of elements came to be.”
Scientists have long theorized that there probably are more elements beyond the periodic table, but their atomic masses render them unstable, so they would quickly decay into lighter elements. That of course makes finding and studying them extremely tricky – the heaviest known element, oganesson, has an atomic mass of 294 u and only five atoms of it have ever been produced in the lab.
The research was published in the journal Science.