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Stellar Death

Explore the lifecycle of stars from birth to their spectacular demise, covering low mass to supernovae and remnants in astronomy. Discover how stars evolve, form planetary nebulae, turn into white dwarfs, supernovae remnants, black holes, and more!

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Stellar Death

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  1. Astronomy 315 Professor Lee Carkner Lecture 14 “I am glad we do not have to try to kill the stars. … Imagine if a man each day should have to try to kill the sun? We were born lucky” --Earnest Hemingway, The Old Man and the Sea Stellar Death

  2. Death Defined • The star can no longer support itself by internal thermal pressure and so: • The details depend on mass

  3. Very Low Mass • Red dwarfs (M < 0.4 Msun) burn their fuel very slowly • Take a very long time (10’s of billions of years) to use up all hydrogen • Red dwarfs will fade away as they run out of fuel • Never become giants since they produce no helium core

  4. Solar Type • Stars with between 0.4 and 4 Msun go through the following phases: • Hydrogen and helium shell burning (asymptotic giant branch) • What happens next?

  5. Evolution of 1 Solar Mass Star

  6. Mass Loss • All stars lose mass • Mass loss is very low for main sequence stars • Giants have higher mass loss rates, due to: • Thermal pulses: changes in the core that cause bursts of energy which can push the outer layers away

  7. Separation • Core gets denser, outer layers get less dense • If the core is hot enough, its radiation will make the ejected outer layers glow

  8. Planetary Nebulae • These glowing ejecta are known as planetary nebulae • Have nothing to do with planets • Composition: low density gas producing emission lines

  9. IC3568 --HST

  10. Mz3 -- HST

  11. Ring Nebula -- HST

  12. Structure of Planetary Nebulae • We would expect planetary nebulae to be spherical • How does spherical star eject mater into a non-spherical shape? • Blocked by companion stars or planets? • Different waves of ejecta interacting?

  13. White Dwarf • The leftover core of the star becomes a white dwarf • There is no fusion going on in a white dwarf so it slowly cools • What supports a white dwarf?

  14. Degeneracy • Electrons obey the laws of quantum physics including the Pauli Exclusion Principle: • Due to its high pressure the core becomes degenerate • Degenerate gas resists compression because electrons cannot be forced any closer together due to the Pauli exclusion principle

  15. White Dwarf Properties • White dwarfs are very dense • Start out hot and then cool • White dwarfs obey the Chandrasekhar Limit • Must be less than 1.4 Msun, or they cannot be supported by electron degeneracy pressure

  16. Sirius A and B

  17. High Mass Stars • Star will become a supergiant with a huge radius (up to 5 AU) but most of its mass in a small earth-sized core of layered elements

  18. Evolutionary Paths

  19. Core Collapse • In a short time (million years or less) the star burns through all elements up to iron • There is no more thermal energy to support the very dense core • Energy from the collapsing core rebounds to produce a supernova

  20. Supernova • A nova is a generic term for a sudden brightening of a star • An exploding massive star is technically known as a Type II supernova • Explosion is almost a billion times more luminous than the sun • Leaves behind a supernova remnant

  21. Supernova 1987a -- Before & After

  22. Supernova 1987a -- Remnant

  23. Anasazi Depiction of 1054 SN?

  24. Crab Nebula -- Optical & X-ray

  25. Post Main Sequence Paths

  26. Stellar Corpses • After a supernova (or the planetary nebula phase) the core of the star gets left behind • Low and medium mass stars leave white dwarfs • Higher mass stars produce neutron stars • Very high mass stars produce black holes

  27. Next Time • Read Chapter 22.1-22.4

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