A new study from Uppsala University has found that the Sun contains 55 percent more silver than previously estimated, a discovery that refines our understanding of the chemical composition of our nearest star and the evolution of the Milky Way. The research, published in the journal Astronomy & Astrophysics, used advanced spectroscopic techniques and a novel atmospheric model to analyze the abundance of silver in the solar atmosphere.
Like most stars, the Sun is composed almost entirely of hydrogen and helium, with only about 1.5 percent of its mass made up of heavier elements such as carbon, iron, and silver. These trace elements are crucial because they act as a fossil record of the cosmos, revealing how stars and planets have formed and evolved over billions of years. Heavy elements are produced inside stars through nuclear fusion and during stellar explosions, which then disperse them into space, making them available as chemical building blocks for new generations of stars and planets.
To determine the amount of silver in the Sun, the researchers analyzed sunlight using spectroscopy. When atoms in the solar atmosphere absorb light, they produce dark absorption lines at specific wavelengths in the spectrum, known as spectral lines. These lines act as unique fingerprints for each element. By comparing these fingerprints with those generated by calculated atmospheric models, scientists can quantify the abundance of elements like silver. Previous estimates relied on simplified models, but the new study developed a more sophisticated approach.
The team combined a dynamic model of the Sun's outer layers with improved atomic physics calculations to capture how silver atoms interact with light and other particles. Unlike earlier methods, the new calculations include non-equilibrium effects, meaning that the light itself influences the silver atoms that produce the absorption lines. This allowed the researchers to interpret the spectral lines with greater accuracy. The new silver abundance resolves a long-standing problem known as the missing silver in the Solar System. Until now, the amount of silver measured in the Sun was significantly lower than that found in chemically primitive meteorites, which formed from the same cloud of gas and dust about 4.6 billion years ago. The new value aligns much more closely with the meteorite data.
Lead author Sema Caliskan, who began her doctoral studies working on atomic structure before applying her expertise to stellar astrophysics, explained that the new model enabled a more precise interpretation of the spectral lines used to determine silver abundance. The results also improve our understanding of how silver and other elements are produced in stars and stellar explosions and subsequently incorporated into new stars and planets. The same method will now be applied to other stars. By studying the light of different types and ages of stars, the team hopes to understand where silver forms in the universe and how it has been distributed across the Milky Way over time.
The study was conducted by S. Caliskan, A. M. Amarsi, P. Jönsson, N. Grevesse, and B. K. Sahoo, and appears in Astronomy & Astrophysics under the title "Ag I model atom and the 3D non-LTE solar silver abundance." The findings underscore the importance of advanced modeling in stellar astrophysics and provide a clearer picture of the chemical history of our galaxy.