The Sun, like most stars, is made almost entirely of hydrogen and helium. Heavier elements, including carbon, iron, and silver, account for only 1.5 percent of its mass. Even in such small amounts, these elements are highly valuable to astronomers because they preserve clues about the history and chemical development of the cosmos.

A PhD Project Reveals a Solar Surprise

"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 created inside stars and during stellar explosions. They are later incorporated into new stars, planets, and other cosmic material. Measuring how much of each element is present helps scientists trace the chemical evolution of the Milky Way.

Reading Silver's Fingerprint in Sunlight

To measure the Sun's silver content, the researchers studied sunlight through spectroscopy. Atoms in the solar atmosphere absorb light at particular wavelengths, leaving dark features in the spectrum called spectral lines. Each element creates its own distinctive set of lines, much like a fingerprint.

Scientists compare these patterns with models of the solar atmosphere to calculate how much of an element is present. Earlier estimates relied on simplified models. In the new study, the team developed a more advanced approach that produced a silver estimate 55 percent higher than before.

The researchers combined a dynamic model of the Sun's outer layers with improved calculations from atomic physics. This allowed them to describe more accurately how silver atoms interact with light and surrounding particles. Unlike previous methods, the new calculations also account for non-equilibrium effects. In this case, the light itself affects the same silver atoms responsible for producing the dark absorption lines.

Solving the Solar System's Missing Silver Problem

"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 revised result addresses a long-standing problem involving silver in the solar system. Previous measurements suggested that the Sun contained significantly less silver than chemically primitive meteorites. That difference was difficult to explain because the Sun and those meteorites formed from the same cloud of gas and dust about 4.6 billion years ago.

With the new calculation, the Sun's silver abundance is now much more consistent with the amount found in these ancient meteorites.

Tracing Silver Across the Milky Way

The findings may also improve scientists' understanding of how silver and other heavy elements are formed in stars and stellar explosions before becoming part of later generations of stars and planets. The researchers now plan to use the same method to study 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 performed with Tetralith, a Swedish supercomputer at the National Supercomputer Center at Linköping University. The project combined expertise in stellar physics and atomic modeling.

Comparable methods have previously been used to study other elements, but this is the first time the approach has been applied to silver in the Sun.