STAR LIFE & DEATH

1. STAR LIFE & DEATH

2. Life on the Main Sequence

3. Life on the Main Sequence • Stable fusion: hydrogen  helium • Accumulation of helium in core • Steady increase in luminosity • 90% of star’s life spent on main sequence • More mass  shorter MS lifetime

4. Main Sequence structure depends on mass . . . pgs. 276

5. Sun Low-mass stars: luminosity increases with age zero-age main sequence Luminosity Temperature

6. Change in composition of 1 solar mass star. Fusion ceases when core converted to helium – star now leaves main sequence.

7. Sun: ~ 10 billion years

8. Star Death I: Low Mass Stars (M < 8M)

9. Red Giant Surface cools, core contracts & heats, radius expands. ‘Evolutionary tracks’ p. 277

10. Vigorous H  He fusion in shell drives envelope outward. Inert helium core (shrinking) Sun as a red giant p. 277

11. Red Giant: Aldebaran T = 3500 K L = 370 L R = 50 R M  3 M 

12. * Core temp 100 million K: Helium fusion begins Another Helium Beryllium Gamma Ray Helium Carbon Gamma Ray

13. In addition . . . 12C + 4He  16O + gamma ray

14. Supergiant Core He exhaustion He ignition Horizontal branch On the HR diagram . . .

15. Helium-burning, Horizontal Branch star p. 279

16. Helium-fusing shell Hydrogen-burning shell Contracting carbon-helium core Supergiant Star

17. Old stellar core Planetary Nebula Ejected stellar envelope Ring Nebula * Supergiants lose mass: > Stellar winds > ‘Flashes’ in helium-burning shell p. 281

19. p. 281

20. Old stellar core shrinking to White Dwarf state. Hourglass Nebula

21. The whole story . . . p. 280

22. Star Death II: High Mass Stars (M > 8M)

23. High temp., rapid fusion on CNO Cycle Again . . . hydrogen fusion ceases when core converted to helium – star now leaves main sequence.

24. core re-ignition core exhaustion Multiple core fusion stages are possible. p. 283

25. Core Fusion Core Temp Duration results in Iron For a 25 M star: H fusion 40 million K 7 million yr He fusion 200 million K 500,000 yr Carbon fusion 600 million K 600 yr Neon fusion 1.2 billion K 1 yr Oxygen fusion 1.5 billion K 6 mos Silicon fusion 2.7 billion K 1 day

26. As fusion ceases . . . ‘Onion Skin’ p. 283

27. Fusion ceases when iron is produced . . . p. 284

28. Iron core contracts, heats Nuclei disintegrate Protons absorb electrons: proton + electron  neutron + neutrino Core stiffens, bounces back slightly Core bounce + neutrino flow ejects envelope: SUPERNOVA!

29. Elements heavier than iron created in blast.

30. Before After Supernova 1987A

32. SN ejecta Stuff ejected before SN. SN 1987A in 1999

33. SN blast wave reaches inner ring

34. Neutrino arrival proton + electron  neutron + neutrino SN 1987A (deep underground)

35. SN probably occur ~ once per 100 yrs in our galaxy.

36. 600 mi/s Pulsar (rotating neutron star) Crab Nebula Supernova Remnant (Exploded 1054 AD) Visible in broad daylight for 23 days in July, 1054!

37. ".. In the 1st year of the period Chih-ho, the 5th moon, the day chi-ch'ou, a guest star appeared south-east of Tien-Kuan [Zeta Tauri]. After more than a year, it gradually became invisible .."

38. Supernova recorded at Chaco Canyon, NM?

39. Cygnus Loop ~13,000 BC

40. Vela Supernova Remnant (~10,000 BC) Interstellar medium ‘seeded’ with heavy elements.

41. Neutron star? Black hole? Cassiopeia A Supernova Remnant X-ray

42. Iron Silicon Cassiopeia A Supernova Remnant