Silver is a strange element to care about if you’re an astronomer. It’s rare, it’s hard to measure in stars, and on Earth we mostly think of it as jewelry. But in the Sun, silver has been sitting at the center of an unsolved puzzle: why does the Sun seem to have noticeably less silver than the meteorites that formed alongside it from the same primordial cloud of gas and dust?

A new study published in Astronomy & Astrophysics by researchers at Uppsala University, Malmö University, the University of Liège, and India’s Physical Research Laboratory offers the most convincing answer yet. By building the first truly realistic computer model of how silver atoms behave in the Sun’s turbulent, roiling atmosphere, the team found that the Sun actually contains more silver than previously thought, enough to close most of the gap with meteorite measurements.

Why silver matters to astrophysicists

Silver isn’t forged in ordinary stellar fusion. Instead, it’s built almost entirely through the “r-process” , rapid neutron capture, a chain of nuclear reactions that briefly occurs in extreme, neutron-rich environments like neutron star collisions. Heavier r-process elements, like gold or europium, show a consistent production pattern across many stars. But lighter r-process elements, silver among them, deviate from that pattern in ways that suggest a second, distinct production channel is at work, nicknamed the “weak” r-process. Because silver sits right in the transition zone, pinning down its abundance precisely, especially in the Sun as a reference point, helps astronomers figure out where and how these elements are actually made.

Silver has an added wrinkle: it’s also what’s called a moderately volatile element, meaning it partially evaporates out of the dust grains that formed meteorites. That makes the Sun-versus-meteorite comparison a useful check on how planets and small bodies actually formed, and on whether the Sun’s outer layers are truly representative of the material the whole solar system was built from.

The problem with the old measurement

Measuring silver in the Sun is unusually difficult. Only two silver absorption lines are visible in the solar spectrum, and both sit in the ultraviolet, a crowded, blend-heavy region where neighboring elements’ spectral lines overlap and contaminate the signal. Previous estimates also relied on simplifying assumptions: treating the Sun’s atmosphere as a smooth, one-dimensional layer in complete thermal equilibrium. Real stellar atmospheres are neither smooth nor in equilibrium, they’re a boiling, granulated surface where hot gas rises, cools, and sinks in complex convective cells, and where radiation can knock atoms out of their expected energy states entirely.

Until now, nobody had modeled silver while accounting for both of these complications together, largely because the necessary atomic physics data simply didn’t exist.

Building an atom from scratch

To fix that, the team assembled what’s called a “model atom” for neutral silver: a detailed map of 57 energy levels and the radiative and collisional pathways connecting them. Some of this data came from laboratory measurements in the NIST atomic spectra database, but many transitions had never been measured at all. The team filled these gaps with quantum-mechanical calculations, including a fresh set of oscillator strengths (a measure of how strongly an atom absorbs or emits light at a given wavelength) computed using an ab initio Hartree-Fock method, and new estimates of how silver atoms interact with the abundant hydrogen atoms surrounding them.

That hydrogen-collision data turned out to be the single largest source of uncertainty in the whole model, more influential than the radiative data, the electron-collision rates, or even the background line opacities the team also tested.

Feeding this model atom into a 3D radiative-transfer simulation of the Sun’s atmosphere, built from a supercomputer simulation of solar convection, the researchers found that both effects, the Sun’s granulated 3D structure and its departure from thermal equilibrium, push the inferred silver abundance in the same direction: upward. Combined, they produce a substantial correction relative to older, simplified analyses.

A closer match with meteorites

After also re-measuring the strength of the two solar silver absorption lines against a high-resolution reference spectrum, and carefully accounting for a blended iron line that had previously thrown off the silver measurement, the team arrived at a new solar silver value that’s about 50% higher (in linear terms) than the previously accepted figure.

That revision shrinks the gap between the Sun’s photosphere and meteorite chemistry from a fairly serious mismatch down to a much smaller, and far less alarming, residual difference, one now consistent with what’s seen for other moderately volatile elements. In other words, much of what looked like a genuine chemical anomaly between the Sun and the building blocks of the solar system turns out to have been a measurement problem all along.

What’s next

The Sun was really just the proving ground here. The team’s real goal is to apply this new silver model to old, metal-poor stars, the fossil relics of the early galaxy, where silver’s abundance pattern can help settle the debate over the “weak” r-process and where the heavy elements powering it actually come from. Because the same physical effects that boosted the Sun’s silver abundance should get even stronger in these ancient, metal-poor stars, the team expects the corrections there to be even larger, potentially reshaping how astronomers read the galaxy’s chemical history.

Source: S. Caliskan et al., “Ag I model atom and the 3D non-LTE solar silver abundance,” Astronomy & Astrophysics, Vol. 711, A155 (2026). Read the full paper: https://www.aanda.org/articles/aa/full_html/2026/07/aa59578-26/aa59578-26.html