AstronomyLesson 1 of 2 in the course The Death of Stars

Low-Mass Stellar Remnants: White-Dwarf Support, Cooling, and Mass Limits

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

This lesson follows a Sun-like star after it has shed its outer layers and its core has exhausted the fuel needed for further fusion. The core’s final collapse reveals how matter behaves at extreme density.

After a Sun-like star has used up the helium in its core, it no longer has a source of energy there to provide pressure against gravity. The core contracts, while the star sheds its outer layers to form a planetary nebula. A final, brief episode of fusion may consume some remaining hydrogen in the outer regions, but a low-mass core cannot become hot enough to begin another sustained stage of fusion.

All flashcards

Pauli exclusion principle
The quantum rule that no two electrons can occupy the same quantum state.
Degenerate matter
Matter in which quantum rules restrict particles from occupying the same states.
Electron degeneracy pressure
Pressure arising from quantum restrictions on electrons that can support a white dwarf without ongoing fusion.
Chandrasekhar limit
The maximum white-dwarf mass, about 1.4M⊙1.4 M_\odot, supportable by electron degeneracy pressure.
White-dwarf mass–radius relation
For white dwarfs, greater mass corresponds to a smaller radius.

Quiz questions

  1. How does a white dwarf’s radius generally change as its mass increases?Answer: Its radius decreases as stronger gravity compresses it more tightly.
  2. What is the approximate Chandrasekhar limit for a white dwarf?Answer: About 1.4M⊙1.4 M_\odot.
  3. What is the main energy source of a white dwarf after sustained fusion ends?Answer: Stored thermal energy that gradually radiates into space.
  4. As a white dwarf cools, how does its position change along the H–R diagram cooling sequence?Answer: It moves toward lower surface temperature and lower luminosity.
  5. Why are black dwarfs not expected to exist yet?Answer: The universe has not existed long enough for white dwarfs to cool fully.

Based on Astronomy 2e by Andrew Fraknoi, David Morrison, Sidney Wolff (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.

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