Researchers at Uppsala University have calculated that the Sun contains 55 per cent more silver than previously estimated. The results are based on more realistic modelling of the Sun's atmosphere and resolve a long-standing problem of missing silver in the solar system.
Like most stars, the Sun consists almost entirely of hydrogen and helium and only 1.5 per cent of its mass consists of heavier elements such as carbon, iron, or silver. Yet, these trace elements are extremely important. They act as a fossil record of the cosmos.
PhD Student Makes Discovery
"The new knowledge about the Sun's composition is important for the understanding of other stars, planets and cosmic material, because the Sun is one of astronomy's key reference points," says Sema Caliskan, who conducted the work during her PhD studies at the Department of Physics and Astronomy at Uppsala University.
Heavy elements are formed in stars and during stellar explosions and become part of new generations of stars and planets. Mapping the abundance of these elements is key to understanding the chemical evolution of the Milky Way.
Spectroscopic Analysis
To determine the amount of silver in the Sun, the researchers analysed sunlight using spectroscopy. When atoms in the solar atmosphere absorb light, they produce dark absorption features at specific wavelengths in the spectrum, known as spectral lines. These lines act as fingerprints, with each element producing a unique pattern.
The fingerprint is compared to calculated atmospheric models to quantify the abundance of silver in the Sun. Previous estimates were based on simplified models. However, in this new study the researchers developed a new model that predicts 55% more silver than before. They combined a dynamical 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 influences the same silver atoms that create the dark absorption lines.
The Solar System's Missing Silver
"With our new model, we were able to interpret the spectral lines used to determine the solar silver abundance more accurately," says Sema Caliskan, who started her PhD studies working on the structure of atoms, and later applied her expertise to problems in stellar astrophysics.
The new silver value resolves a long-standing problem of missing silver in the solar system. Until now, the silver abundance measured in the Sun was significantly lower than that found in chemically primitive meteorites, which both formed at the same time from the same cloud of gas and dust 4.6 billion years ago. The new silver value in the Sun is now in much better agreement with these meteorites.
Method Could Be Used on Other Stars
The new results also improve our understanding of how silver and other elements are produced in stars and stellar explosions and later incorporated into new generations of stars and planets. The same method will now be applied to other stars.
"By studying the light of stars of different types and ages, we hope to understand where silver is formed in the universe, and how it has been distributed throughout the Milky Way over time," says Sema Caliskan.
About the study The calculations were carried out using the Swedish supercomputer Tetralith at the National Supercomputer Centre at Linköping University, bringing together expertise in stellar physics and atomic modelling. Similar methods have been applied to other elements, but this is the first time it has been used to analyse silver in the Sun.
