1. Star Stuff Joy Harjo (1951 – ) from Secrets From the Center of the World I can hear the sizzle of newborn stars, and know anything of meaning, of the fierce magic emerging here. I am witness to flexible eternity, the evolving past, and know I will live forever, as dust or breath in the face of stars, in the shifting pattern of winds.

2. WHAT DO YOU THINK? 1.How do stars form? 2.Are stars still forming today? If so, where? 3.Do more massive stars shine longer than less massive ones? What is the reason?

3. Key Questions to Answer!  What is the interstellar medium made of? How do stars form? How do we know?  How will our Sun evolve as a star? What will its final state be? Compare its predicted evolution to that of higher-mass stars. How do they end? How do we know?

4. The “Dark Tower” in Scorpius

5. The Pillars of Creation near Orion

6. Pleiades in Visible light

7. Pleiades in IR light “false” colors, applied to match temperatures

8. The Inter-stellar Medium  Observe/Research  Where do stars form?  What are they made of?  What properties are common? Rare?  Create THEORY of star formation  Test hypotheses predicted by the theory

9. The ISM: How do we know?  Where do stars form?  Visible, IR, Microwave, Radio observations  What are they made of?  Spectra  What properties are common? Rare?  HR Diagram, Mass, Number density, Location  Test hypotheses predicted by theory  Visible, IR, Microwave, Radio observations

10. ISM: Where do stars form? We observe:  Visible “extinction nebulae” block background light  Visible emission nebulae form hot gas  Visible signs of dust scattering and dimming and reddening starlight

11. Extinction nebulae from gas/dust blocking light

12. Emission nebulae from gas emitting light Extinction nebulae from gas/dust blocking light

13. Reflection nebulae from dust scattering blue light

15. The Horsehead Nebula

17. Dust grains also cause “interstellar reddening”

19. Learning About Stellar Lives  How can we know anything?  Create HR diagrams of clusters of stars  Assume  Same relative distance  comparing relative brightness is fair  Same relative age  comparing masses and types of stars is fair

20. Pleiades “Open” Cluster in disk of Milky Way Galaxy

21. Pleiades HR Diagram Stars of all types & masses

22. Another Star Cluster Stars of all types & masses

23. NGC 2264 HR Diagram Some objects not yet formed as stars! “T-Tauri Protostars”

24. Observational evidence of “protostars”

25. Protostars seem to appear in CLUSTERS

28. New Stars & Brown Dwarfs that will never be…

29. An actual Brown Dwarf!

30. Supermassive stars lead very unstable lives! Pressure from fusion literally blows outer layers away!

31. One of the largest stars known…. 5,000,000 times brighter than our Sun!

32. Star Formation in 4 Steps! Start with Large Cloud of Gas & Dust 1.Shock creates fragments & “blobs” 2.Gravity creates clusters of star “seeds” 3.Individual blobs heat up and glow as protostars 4.Protostars start fusion in cores 5.♫ A star is born!  ♫

33. Star Formation in 4 Steps!  Start with Large Cloud of Gas & Dust  Giant molecular clouds  Raw materials to form 100’s, 1000’s, or millions of stars in clusters.  Mass & Location affect # of stars to be formed  Temperature affects rate of formation  Observations supporting this phase:  Radio telescopes, Microwave Maps

35. Star Formation in 4 Steps! 1. Shock the cloud – break it into fragments  Gravitational Forces (galaxies, mergers, collisions)  Stellar winds of new massive stars  Supernovae of massive stars that form fast  Observations supporting this phase:  HST views of Eagle Nebulae

39. Star Formation in 4 Steps! 2. Gravity takes over, creating clusters of what will eventually be stars  OB Associations  Open Clusters  Globular Clusters Observations supporting this phase:  Microwave/IR observations of warming regions

41. Star Formation in 4 Steps! 3. Individual blobs heat up, rotate, and glow as protostars  Contracting into disks  Shining by gravitational energy (not fusing!)  Larger than “real” stars, & cooler  Develop jets of radiation from poles Observations supporting this phase: T-Tauri stars

42. Disks & Jets in Protostars

43. Star Formation in 4 Steps! 4. A star is born!  Fusion of Hydrogen to Helium starts in core  Stops Contracting  Hydrostatic Equilibrium Established  A “main sequence” star But…. Will it have planets?

44. Star Formation in 4 Steps!

45. Lives of Main Sequence Stars  Where a star is plotted depends on mass  O dwarfs (O V) are most massive  M dwarfs (M V) are least massive  ALL Main Sequence stars fusing H  He

46. Lives of Main Sequence Stars  ALL Main Sequence stars fusing H  He  The star is stable, in balance  Gravity (in) vs. force (out) from gas pressure and radiation pressure from fusion reactions

47. Stellar Evolution  Building models of what happens to stars  Low mass (0.08 to 0.4 M sun  Medium mass (0.4 to 4+ M sun  Higher Mass (5+ to >100 M sun

48. Low mass star evolution (~8% to ~40% of our Sun’s Mass)  Slower fusion reaction rate  Cooler surface temp (red stars)  Low Luminosity  Longer Lives  “Economy models!”

49. Low mass star evolution models  Totally “convective” inside! (mixed throughout)  convert ALL Hydrogen into Helium  don’t develop a Helium “core”  Eventually collapse to white dwarf

50. Low mass stars models predict mixing inside to convert all H to He

51. Medium Mass 40% to 400% of Sun’s Mass  Life like our Sun – about 10 Billion years  Slowly develop Helium core  Helium “ash” not fusing --- yet!  Surrounded by Hydrogen still fusing

52. Medium Mass 40% to 400% of Sun’s Mass  Core collapses, becomes “degenerate”  Star swells into Red Giant  Eventual Helium FLASH as fusion of He  Carbon starts up!  A “new” life– for a short time!

56. High Mass Stellar Evolution  Much greater fusion rate, MUCH brighter, MUCH, MUCH shorter lived stars  Quickly reach Helium Core stage, and can start fusing He  Carbon, develop C core, then repeat with heavier and heavier atoms

57. High Mass Stellar Evolution  “Onion Skin” model of heavier & heavier shells  Fuse until Iron core formed…  Boom!