NEWS – A groundbreaking study published in Nature has provided direct evidence for the long-theorized shell structure of massive stars.

HIGHLIGHTS

What is it?

• Massive stars, more than eight times the mass of the Sun, evolve with a layered “onion-like” structure.
• Fusion occurs in successive shells:
  • Outer layers: Hydrogen, Helium
  • Deeper layers: Carbon, Oxygen, Neon, Magnesium
  • Innermost layers: Silicon, Sulphur
  • Core: Inert Iron

Theoretical Model

• For decades, astrophysicists explained stellar evolution using this shell-based structure.
• While outer shells (hydrogen, helium) had been indirectly observed in Wolf-Rayet stars and some supernovae, deeper layers remained elusive.

The Breakthrough Study

• Published in Nature, based on data from the Zwicky Transient Facility (ZTF) and ground-based telescopes.
• Observed a rare supernova, SN 2021yfj.
• Light from this explosion carried spectral signatures of silicon and sulphur, elements formed just outside the iron core.
• Indicates the progenitor star had been stripped to its innermost layers before collapse.

Significance of the Finding

1. Direct Confirmation of Stellar Shell Model
   • Offers rare, concrete evidence that stars truly follow the concentric shell model all the way to the iron core, not just in outer layers.
2. Discovery of a New Supernova Class
   • Identified as Type Ien supernova.
   • Defined by silicon- and sulphur-rich circumstellar material.
   • Extremely rare: only one detected in six years of continuous sky survey.

Why it Matters?

• Enhances understanding of stellar death cycles and elemental creation in the universe.
• Provides insight into how heavy elements, essential for planets and life, are distributed across galaxies.
• Reinforces the role of supernovae as cosmic forges of matter.