Heaviest Chemical Elements Created by Ancient Stars

Like most people, all my high school science classrooms had one wall papered with a huge, multi-coloured chart. It was, of course, the Periodic Table of the Elements.

Readers who were paying extra-close attention in their chemistry classes may remember that Dimitri Mendeleev came up with the periodic table in 1869. He organized the known chemical elements into a chart, based on their atomic masses and properties.

Mendeleev left gaps in the table for elements that hadn’t been discovered yet. The resulting table is a foundation of science that chemists still use, with some revisions, every day. 

‘We Are Made of Star Stuff’

There’s a popular saying that “we are made of star stuff.” The phrase comes from Carl Sagan, and he was referring to the fact that stars generate all of the universe’s chemical elements through a process called nucleosynthesis.

Dr. Ian Roederer is an associate professor at North Carolina State University. He’s been studying nuclear astrophysics using stellar chemistry for the past 13 years.

Professor Roederer is particularly interested in understanding the origin of the heaviest chemical elements, and our Milky Way galaxy’s formation. He’s earned a reputation as an expert in the rapid neutron capture process (r-process) by which stars generate the elements with the highest atomic mass.

Rapid Neutron Capture Process (R-Process)

The r-process begins with an atomic nucleus surrounded by a sea of neutrons. In the blink of an eye, a group of neutrons join that nucleus.

Some of those free neutrons decay into protons. This increases the atom’s mass. The result ends up as one of the heaviest chemical elements like gold, platinum or uranium.

Professor Roederer is the lead author of a study the journal Science published this week. The study found that ancient stars could produce elements with atomic masses of more than 260, heavier than any natural element we find on Earth.

Elements Well-Known Stars Produce Through Fission

The scientists wanted to find out more about the elements that well-known older stars produce through nuclear fission. They were hoping this would shed some new light on how the r-process creates these heavier elements.

The heaviest chemical elements are also highly unstable. They decay into lighter elements through nuclear fission, which is why we don’t usually encounter them in our daily lives on Earth.

“We have a general idea of how the r-process works, but the conditions of the process are quite extreme,” Professor Roederer explained. “We don’t have a good sense of how many different kinds of sites in the universe can generate the r-process, we don’t know how the r-process ends, and we can’t answer questions like, how many neutrons can you add, or how heavy can an element be?

To try to answer those questions, the researchers selected a sample of 42 familiar Milky Way stars. They knew these stars contained some of the heaviest chemical elements that earlier stellar generations had produced through the r-process.

Looked Across Star Sample’s Total Element Volume

Instead of looking at these stars individually, as scientists have done in the past, the team took a broader view. They looked across the stars’ population to determine the total volume of each element, taking all of the sampled stars as a whole.

The scientists discovered some of the elements we see near the middle of the periodic table like sliver and rhodium because of the fission, or splitting, of the heaviest chemical elements. Based on that finding, they calculated that the r-process can produce atoms with an atomic mass beyond 260 before nuclear fission occurs.

This discovery has important implications for humanity’s grasp of astrophysics and cosmology. It helps scientists fill in more of those gaps that Mendeleev left in his table back in the 19th century.

New Insights Into Nucleosynthesis

The findings also offer new insights into the nucleosynthesis process, and how it creates elements in some of the universe’s most extreme environments. Understanding these processes can help scientists work out the limitations and “rules” governing the process.

Most importantly, since all matter in the universe comes from nucleosynthesis processes, understanding the formation of the heaviest chemical elements gives us new insights into the cosmos as a whole. Scientists can gain more profound insights into the evolution of galaxies, stars, planets and life from these findings.

These discoveries about how the heaviest chemical elements form are another step toward uncovering the new, science-based story humanity needs about the universe and our place within it. Grasping the processes taking place in these distant stars helps us to gain a better understanding of our own nature and the planet we all share.

And Another Thing…

We tend to think of other planets, stars and galaxies as outer space. When scientists share their findings about nucleosynthesis, they remind us that we’re all part of a single, interconnected cosmos where every atom and molecule forms in the same way.

The next step for Professor Roederer and his team is to apply this new understanding about the heaviest chemical elements, with masses beyond 260, to the rest of the Periodic Table. Why are there so many elements, and how did they all result from these astrophysical processes?

“That 260 is interesting because we haven’t previously detected anything that heavy in space or naturally on Earth, even in nuclear weapon tests,” Professor Roederer concluded. “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.”

We always have more to learn if we dare to know.

Learn more:

Ancient Stars Made Extraordinarily Heavy Elements

Element abundance patterns in stars indicate fission of nuclei heavier than uranium

Where Do Heavy Metals Come From?

Where Do Heavy Metals Come From? Encore Set

Primordial Universe Made of Strange Particles