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How Stars Die: White Dwarfs, Neutron Stars, and Supernovae
Context
The life and death of stars are crucial for understanding the evolution of the universe. Stars produce the elements essential for life through nuclear fusion and distribute them during their deaths. Depending on their mass, stars may end as white dwarfs, neutron stars, or undergo supernovae, contributing to cosmic chemical enrichment and the formation of new stars and planets.
Stellar Lifespan:
- Stars, though seemingly eternal, have finite lifespans determined primarily by their mass.
- Their lifecycle is governed by the balance between:
- Gravitational collapse (inward force)
- Pressure from nuclear fusion (outward force)
Nuclear Fusion: The Source of Stellar Energy:
- In the stellar core, hydrogen nuclei fuse into helium under extreme temperature and pressure.
- This process releases tremendous energy that supports the star against gravitational collapse.
- In 1938, Hans Bethe formulated the fusion mechanisms powering stars, earning the Nobel Prize in Physics.
Death of Low to Medium Mass Stars (Like the Sun)
- When hydrogen in the core is exhausted:
- Fusion slows down, and the core contracts under gravity.
- If core temperature exceeds ~100 million Kelvin, helium fusion begins, producing carbon and oxygen.
- Once helium is also exhausted:
- The outer layers are ejected gently, forming a planetary nebula.
- The remaining core becomes a white dwarf:
- Extremely dense and hot.
- Roughly Earth-sized.
- Composed primarily of carbon and oxygen.
- Nearly 95% of stars in a typical galaxy end their lives as white dwarfs.
PYQ1. With reference to the ‘Proxima Centauri’, consider the following statements:
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