New research suggests that cosmic fission may have played a role in the creation of heavy elements. Analysis of ancient stars shows a correlation between light metal and rare earth nuclei, suggesting the creation of superheavy nuclei beyond the known periodic table of elements. This discovery confirms the theory of cosmic fission and shows the existence of elements with an atomic mass of 260, expanding our understanding of the universe.
Fission models discovered clear fingerprints of nuclear processes that have never been directly observed in stars before.
Elements above iron in the periodic table are thought to have been created in the Big Bang, such as the merger of two neutron stars or in a rare supernova. New research suggests that fission may be the process by which heavy elements are created in the universe. Researchers combed through data on various elements present in very old stars and discovered potential signatures of fission, suggesting that nature likely produces superheavy nuclei beyond the heaviest elements in the periodic table.
"People have always thought that fission occurs in the universe, but so far, no one has been able to prove it," said Matthew Mumpower, a theoretical physicist at Los Alamos National Laboratory and co-author of a paper describing the research in Science.
Mumpower said researchers used the latest observations to find a connection between lightweight precision metals such as silver and the nuclei of rare earth atoms such as europium. When one set of elements goes up, the corresponding element in the other set goes up too - the correlation is positive.
'Incredible' evidence of fission
"The only possibility for this to occur in different stars is if there is a consistent process in the formation of heavy elements," Mumpower said. "The team tested all possibilities, and fission was the only explanation that could reproduce this trend. This is incredibly profound and the first evidence of fission operating in the universe, confirming a theory we proposed several years ago. As we get more observational data, the universe is saying, hey, there is a signature here, and it can only come from fission."
Research also suggests that elements with an atomic mass (number of protons plus number of neutrons) of 260 may exist, which would be heavier than elements at the higher end of the periodic table.
Mumpower developed the fission model used to predict and guide observational findings, led by study author Ian Roederer of North Carolina State University.
Astrophysicists have long believed that heavy elements other than iron are formed when stars explode in what are called supernovae, or when two neutron stars merge. As the name suggests, the latter consists mainly of neutrons, which together with protons make up the nuclei of all atoms. Through a rapid neutron capture process called the "r-process," atomic nuclei grab neutrons to form heavier elements. Whether some atoms become too heavy to stay together and split, or fission, forming two atoms of a lighter but still heavy element (and releasing enormous amounts of energy), has been a mystery for half a century.
In a 2020 paper, Mumpower predicted for the first time the fission fragment distribution of r-process nuclei. Subsequently, a study led by TRIUMF collaborator Nicole Vassh predicted the co-production of lightweight precision metal and rare earth nuclei. The co-production of elements such as ruthenium, rhodium, palladium and silver, as well as elements such as europium, gadolinium, dysprosium and holmium, can be tested by comparing predictions to elemental abundances in stellar ensembles.
The new analysis, led by Roederer, combed through observational data from 42 stars and found exactly the predicted correlation. This pattern provides a distinct signature of the fission production of these elements, as well as similar patterns for slightly heavier and taller elements in the periodic table.
"In r-process-enhanced stars for which we have sufficient data, this correlation is very strong. Whenever nature produces a silver atom, it also produces proportionally heavier rare earth nuclei. The compositions of these groups of elements are in sync," Mumpower said. "We have shown that only one mechanism is responsible - fission, and people have been wrestling with this since the 1950s."
From "Inventory Management" to "Starry Sky"
"At Los Alamos, we developed nuclear fission models because we couldn't measure everything relevant to weapons research as part of the lab's mission," Mumpower said. "These models allow physicists to explain experiments and fill in the data when measurements are lacking. Experimental data on fission have been limited since the United States stopped testing nuclear weapons in 1992. The models perform very well compared to measured data, so in the absence of measurements The model's extrapolations are credible given the data. Studying the formation of heavy elements requires nuclear input of short-lived and long-lived species. Fission yields are the product of a process that splits relatively heavy atoms into lighter atoms - the same process used in nuclear weapons and reactors."