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12.4 Summary of Stellar Lives

Discover how a star's mass shapes its life stages, from main sequence to supernova explosions. Explore the differences in low-mass and high-mass star lifecycles, including the impact of close companions.

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12.4 Summary of Stellar Lives

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  1. 12.4 Summary of Stellar Lives • Our Goals for Learning • How does a star’s mass determine its life story? • How are the lives of stars with close companions different?

  2. How does a star’s mass determine its life story?

  3. Low-Mass Star Summary Main Sequence: H fuses to He in core Red Giant: H fuses to He in shell around He core Helium Core Burning: He fuses to C in core while H fuses to He in shell Double Shell Burning: H and He both fuse in shells 5. Planetary Nebula leaves white dwarf behind Not to scale!

  4. Reasons for Life Stages • Core shrinks and heats until it’s hot enough for fusion • Nuclei with larger charge require higher temperature for fusion • Core thermostat is broken while core is not hot enough for fusion (shell burning) • Core fusion can’t happen if degeneracy pressure keeps core from shrinking Not to scale!

  5. Life Stages of High-Mass Star Main Sequence: H fuses to He in core Red Supergiant: H fuses to He in shell around He core Helium Core Burning: He fuses to C in core while H fuses to He in shell Multiple Shell Burning: Many elements fuse in shells 5. Supernova leaves neutron star behind Not to scale!

  6. Life of a 20 MSun star Life of a 1 MSun star

  7. How are the lives of stars with close companions different?

  8. Thought Question The binary star Algol consists of a 3.7 MSun main sequence star and a 0.8 MSun subgiant star. What’s strange about this pairing? How did it come about?

  9. Stars in Algol are close enough that matter can flow from subgiant onto main-sequence star

  10. Star that is now a subgiant was originally more massive As it reached the end of its life and started to grow, it began to transfer mass to its companion Now the companion star is more massive

  11. What have we learned? • How does a star’s mass determine its life story? • A star’s mass determines how it lives its life. • Low-mass stars never get hot enough to fuse carbon or heavier elements in their cores, and end their lives by expelling their outer layers and leaving a white dwarf behind. • High-mass stars live short but brilliant lives, ultimately dying in supernova explosions. • Sun

  12. What have we learned? • How are the lives of stars with close companions different? • When one star in a close binary system begins to swell in size at the end of its hydrogen-burning life, it can begin to transfer mass to its companion. This mass exchange can then change the remaining life histories of both stars. • Sun

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