UPSC CURRENT AFFAIRS – 08th April 2025

Home UPSC Current Affairs New Insights into Iron Opacity in the Sun

New Insights into Iron Opacity in the Sun

Why in News?

Recent tests have demonstrated that the opacity of iron under solar conditions is much greater than previously approximated, calling into question current solar models.

Introduction

Stars are the drivers of the universe — they give us light and energy, define planetary systems, and impact galactic structure. Among them, the Sun is the most examined object because it’s relatively close to our planet.
But with half a century of observations and advanced modeling, essential inconsistencies persist in our picture of its internal characteristics.
A recent scientific breakthrough has shed new light on a long-standing mystery in solar physics — the role of opacity in explaining elemental abundances and energy transport within the Sun.

Why Study the Sun?

Scientists study the Sun at two levels:

Theoretical Understanding: By observing electromagnetic radiation, solar flares, sunspots, and charged particles, researchers test and refine theories that explain solar processes.
Stellar Models: The Sun is used as a standard for simulating other stars. These models mimic:
- Heat and energy production
- Magnetic fields and stellar rotation
- Sunquakes and solar flares
- Evolution of the stellar atmosphere
- Star cluster and galaxy formation
- Knowledge of stellar behavior assists scientists in deciphering the structure and evolution of the universe.

The Opacity Discrepancy in Solar Models

Until the mid-2010s, solar models consistently predicted 30–50% less carbon, oxygen, and nitrogen in the Sun than had actually been observed.
This was a basic problem since solar models, although intricate and supercomputer-dependent, had otherwise been successful at predicting.

Solar brightness

Initially, scientists suspected measurement errors in elemental abundances. In 2015, a groundbreaking study suggested that the opacity (i.e., energy absorption) of certain elements, particularly iron, was underpredicted.

Key Findings: Iron's Opacity Up to 400% Higher

Scientists exposed iron’s plasma to solar-like conditions near the radiation-convection boundary (around 30% within the Sun’s radius). Results indicated:

Iron’s opacity was 30–400% greater than theoretical expectations
Opacity variations according to radiation frequency
A 15% rise in mean opacity would resolve the abundance discrepancy
That is, errors in how much energy elements such as iron absorb will skew solar model predictions.

Helioseismic and Experimental Reinforcement

These results have been confirmed by recent research with helioseismic data (helioseismology, the study of sound waves within the Sun) and laboratory experiments:

Seismic opacity profiles indicated ~10% more opacity than theory at 2 million K, although lower by 35% than some recalculated models.
Sandia National Laboratories scientists utilized cutting-edge ultrafast X-ray spectrometry to measure the opacity of changing plasmas with previously unprecedented accuracy.
This verified that temporal gradients in the plasma were not a possible explanation for the model-data discrepancy — the issue resides in theoretical opacity assumptions.

Technological Challenges and Future Directions

To measure opacity under conditions similar to the Sun requires:

Electron energies ≥ 180 eV
Particle densities > 30,000 billion billion per millilitre
Employment of magnesium tracers to derive energy and density
Precise measurement of line optical depth (shadow darkness) to make an estimate of radiation absorption
The second step is absolute opacity measurements with formal uncertainty estimates, which are now being researched.

Astrophysics and Cosmology Significance

Solving the opacity problem will enhance solar models so that solar activity can be predicted better.
Improved stellar models can be used to model star formation, planetary system dynamics, and galactic evolution with precision.

Facilitates the understanding of exoplanet habitability, star lifecycle, and element formation in the universe.