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LIFECYCLES OF STARS

Explore the different stages of star evolution, including star formation, main sequence, red giants, planetary nebulae, white dwarfs, and supernovae. Learn about the properties and behaviors of different types of stars.

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LIFECYCLES OF STARS

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  1. LIFECYCLES OF STARS Option 2601

  2. Stellar Physics • Unit 1 - Observational properties of stars • Unit 2 - Stellar Spectra • Unit 3 - The Sun • Unit 4 - Stellar Structure • Unit 5 - Stellar Evolution • Unit 6 - Stars of particular interest

  3. Unit 5 Stellar Evolution

  4. Stellar Evolution • Star formation • Main sequence • Stellar clusters (open, globular) • Population I & II stars • Red Giants • Planetary Nebulae • White Dwarfs • Supernovae • Neutron Stars

  5. Sequence • Protostar • Pre-main Sequence (PMS) • Main Sequence • Post-main Sequence

  6. Protostars • Stars born by gravitational contraction of interstellar clouds of gas and dust • Gravitation energy  50% thermal & 50% radiative • Cloud is a Protostar before hydrostatic equilibrium is established

  7. Protostars • Collapse starts in “free fall” • Particles do not collide during collapse • i.e. P=0, gravity is only force involved • Collapse is uneven • Core collapses more rapidly forming a small central condensation • Core then accretes material

  8. Protostars • Low mass objects accrete all (most) of material • High mass objects behave similarly, but • Fusion begins before end of accretion • Some material then blown away by radiation pressure

  9. Effect of Rotation • If angular momentum > 0 • Cloud flattens into a disk • In some cases several central blobs form, which can coalesce into fewer… • Multiple star systems

  10. Cloud Collapse

  11. Star Formation

  12. Star Formation

  13. Star Formation

  14. Pre-main sequence for a solar mass star

  15. Evolution of a high mass star

  16. Star Formation

  17. Star Formation

  18. Stellar Lifecycle

  19. The Main Sequence • Start of nuclear burning  zero-age main sequence • As H  He composition () changes, structure changes • Rates of evolution depend on two things • Initial mass • Composition

  20. The Main Sequence • High mass stars are hotter & more luminous • Use their energy faster, i.e. evolve faster • Spend less time on the main sequence • O & B stars evolve faster than M stars

  21. Mass-luminosity relation: Giving star lifetime: Quantitatively

  22. Eagle Nebula

  23. Eagle Nebula

  24. Rosette Nebula

  25. T

  26. The Pleiades

  27. Population I Stars • Accreting from the ISM now! (i.e. recent past) • Typical stars are young, in galactic spiral arms where gas and dust found • Typically reside in open star clusters • ~2% of mass elements heavier than H or He (ISM enriched by supernovae) • If M* a little > M energy generation is by CNO cycle • Sun is population I

  28. Post main-sequence for a solar mass star

  29. Evolutionary phases of a solar mass star, post main-sequence

  30. End of Main Sequence

  31. Post main-sequence for a solar mass star

  32. Population II Stars • First stars to be formed in Universe • Have only 0.01% heavy elements • Typically found in galactic bulge and globular clusters • Similar sequence of evolution but occupy different region of H-R diagram during core He burning • Significant temperature changes, heating and then cooling

  33. Late in the life of a solar mass star

  34. Red Giant > PN

  35. Evolutionary phases of a solar mass star, post main-sequence

  36. Late in the life of a solar mass star

  37. PN > White Dwarf

  38. White Dwarfs

  39. For a degenerate gas (non-relativistic): Constant For a perfect gas: From hydrostatic equilibrium:  Greater mass, smaller radius Chandrasekhar Limit White dwarfs form from stars with M  8MSun Degenerate gas pressure prevents further gravitational contraction Chrandrasekhar limit: degeneracy pressure can only support M  1.4MSun. Above this limit a neutron star is formed

  40. White dwarf companions e.g. Sirius – companion Sirius B (Alvan Clark, 1862) Procyon – Procyon B (1882) In binaries we can measure the companion’s mass from Kepler’s laws MSirius B = 1.0MSun TSirius A = 10,000K ; MV = -1.5 TSirius B = 25,000K ; MV = 8 From : R  7  10-3RSun   = 3  109kg m-3 3  10-3LSun

  41. Massive Stars • Stars with masses > 7 M • Masses greater than ~ 50 M • Affected by mass loss (i.e. winds) • As mass of star changes so does the structure and luminosity

  42. Evolution of a high mass star

  43. Evolutionary phases of a massive star

  44. Evolution of a high mass star

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