Almost all of the observable matter in the universe is made of particles that were once inside stars long ago. As massive self-luminous celestial bodies of gas, stars are considered factories of elements that constantly fuse or split to create other lighter or heavier elements.
The weight of elements is referred to as their atomic mass. Broadly speaking, atomic mass is based on the number of protons and neutrons found inside the nucleus of one atom of that element.
Nature of Heavy Elements
Scientists believe the heaviest elements are only created in neutron stars through rapid neutron capture, also known as r-process. This can be visualized as a single atomic nucleus that floats in a soup of neutrons. Suddenly, a group of these neutrons get stuck to the nucleus quickly, allowing them to undergo internal neutron-to-proton changes. Heavy elements like uranium, platinum, and gold form from this process.
Heavy elements are unstable or radioactive, meaning they decay over time. This happens through fission, where a large atom splits into smaller atoms. To make heavier elements like bismuth and lead, the r-process is necessary. This involves quickly adding many neutrons, which must be done using much energy and neutrons. The best place to find them both is at the birth or death of a neutron star or during the collision of neutron stars, leading to the production of raw ingredients needed for the process.
Heavy Elements From Rapid Neutron Capture
Researchers from North Carolina State University have a general idea of how the r-process works, but the conditions needed to carry it out are quite extreme. The experts do not understand how many different regions in the universe can generate this process. They also cannot answer the question as to how the r-process ends, and many neutrons must be added.
To gain a better insight into the r-process, the team decided to look at elements that can be created by fission in some of the well-studied old stars. The team, led by NCSU physics associate professor Ian Roederer, investigated the amounts of heavy elements present in 42 stars in the Milky Way galaxy. The study reported their findings: "Element abundance patterns in stars indicate fission of nuclei heavier than uranium."
These well-studied stars are known to contain heavy elements formed by the r-process during their younger stages. Roederer and his colleagues took a broader view of the amounts of each heavy element, allowing them to identify previously unrecognized patterns. This was made possible by studying the stars collectively rather than individually, as is more common.
The observed patterns indicate that some elements located near the middle of the periodic table, like rhodium and silver, were possibly the remnants of heavy elements that resulted from fission. The experts discovered that the r-process can create atoms with an atomic mass of at least 260 before splitting apart.
According to Roederer, such discovery is interesting because we scientists have not previously detected anything that heavy in space. Here on Earth, those kinds of extremely heavy elements do not occur naturally or are created even in nuclear weapon tests. Seeing these elements in space can guide experts in reconsidering atomic models and fission. Additionally, this discovery can give new insights into how the rich diversity of elements came to be.
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