Scientists have discovered clues to a new world of elements beyond the periodic table. A new study finds that ancient stars may have been producing extremely heavy elements that were unknown to science. The rich diversity of elements in today's universe is thanks to stars. These cosmic factories take elements from their environment and fuse them together to create new elements, and when the stars eventually die, they spread the fruits of their labor throughout the universe. This gives the next generation of stars a more advanced starting point, allowing them to produce more and heavier elements.
But what are the limits of this process, and how heavy can an element be? These questions are the focus of new research by scientists at North Carolina State University.
The weight of elements is determined by their atomic mass, which is defined as the number of protons and neutrons in the nucleus of a single atom of the element. The heaviest naturally occurring element is uranium, with an atomic mass of 238.
The heaviest elements are created through the so-called "r-process," which can only occur in the extreme environments of neutron stars. Essentially, atomic nuclei floating in a star are flooded with neutrons within a fraction of a second, and some of those neutrons are then converted into protons. This creates atoms of heavy elements such as platinum or uranium.
"If you want to make elements heavier than lead and bismuth, then the r-process is necessary. Many neutrons have to be added quickly, but the problem is that doing so requires a lot of energy and neutrons. And the best place to find both is when a neutron star is born or dies, or when neutron stars collide and create the original ingredients for this process."
The team studied the composition of 42 well-studied stars in the Milky Way that are known to contain heavy elements formed in early stars. Rather than studying each star individually, the researchers collectively studied element abundances across entire stellar populations and discovered patterns that had previously been ignored.
The researchers found that certain elements, including ruthenium, rhodium, palladium and silver, were abundant in these stars, but the elements immediately next to them on the periodic table did not have the same correlation. The team says this proves these elements were formed by the decay of heavier elements. The researchers worked backwards and calculated that the atomic mass of the starting heavy element was at least 260u.
"The number 260 is interesting because we haven't detected anything this heavy naturally in space or on Earth before, even in nuclear weapons tests," Rodler said. "But seeing them in space provides guidance on how we think about models and fission -- and can give us insight into how the rich diversity of elements is formed."
Scientists have long believed that there may be more elements outside the periodic table, but their atomic masses make them unstable, so they quickly decay into lighter elements. Of course, this also makes finding and studying them extremely tricky - the heaviest known element, Oganesson, has an atomic mass of 294u, and only five atoms of this element have ever been produced in the laboratory.
The research was published in the journal Science.