Iron Opacity in the Sun: Sandia Study Challenges Solar Models
Why in the news
A fresh laboratory study reported that iron is much more opaque under solar conditions than theory says, raising doubts about current models of the sun and other stars.
Key facts
- Opacity measures how much light a material absorbs rather than lets through.
- Models of the sun must get element abundances and opacities right to predict brightness, neutrino output and magnetic activity.
- Studies since the mid-2010s found the sun has 30-50% less carbon, nitrogen and oxygen than models assumed.
- A 2015 test reproduced sun-like plasma and saw iron opacity up to 400% higher than predicted.
- The March 3, 2025 paper in Physical Review Letters used Sandia National Laboratories facilities: a thin iron sample was hit with X-rays and its shadow read by ultrafast spectrometers.
Experimental conditions
| Requirement | Level |
|---|---|
| Plasma density | Above 30,000 billion billion particles/mL |
| Electron energy | Above 180 eV |
| Imaging speed | Over a billion frames per second |
| Tracer element | Magnesium, to check plasma temperature and density |
Implications
- Opacity governs energy transport and the sun’s internal structure.
- Wrong values distort simulations of stars, galaxy evolution and exoplanet conditions.
Next steps
- Measure absolute transmission, add formal uncertainty estimates, and follow opacity over time in changing plasma.
- Resolution matters for space weather and galaxy formation forecasts.
Exam angle
- Opacity: degree of light absorption.
- Lab: Sandia National Laboratories; journal: Physical Review Letters.
- Tracer element used: magnesium.