Read before class: Star Birth Chapt 18 and 19 Stellar Evolution M ~1 Msun (PN & WD): Chapt 20

1. Lecture 22 – Stellar Evolution HST: Pne - Red Rectangle Star Fleet Academy Tues: Nov 4, 18, 25 Noon Alllen 326 Couldn’t get into PHYS 1830? Enrollment limit has increased. • Read before class: • Star Birth Chapt 18 and 19 • Stellar Evolution M ~1 Msun (PN & WD): Chapt 20 • massive star death (SNe): Chapt 21 • stellar populations Chapt 23 (p. 587) • Gamma-ray bursts & black holes Chapt 22 – REVIEW GR model of gravity Come take up your test. Monday 3pm Allen 514 or by appointment (email about time).

3. STAR

4. Stellar Evolution: Star Death • Recall Stefan-Boltzmann Law • r == stellar radius • T == surface temperature

5. Leaving the MS • H converted to He in core  no pressure P to counter gravity

6.  Red Giant

7. Helium fuses  Carbon • Equilibrium • Horizontal Branch on HR diagram

8. What will happen? Part way through the evolution of 1 solar mass – last lecture to here.

12. Planetary Nebula (PN, plural Pne): • UV photons from core ionize expanding shell • Gas disperses ~3*10**4 yr • Remnant of PN  White Dwarf

13. White Dwarf (WD): • Remnant of PN • size of Earth, mass of ½ sun • initially hot but not luminous • r contraction stops, supported by electron degenerate P • T decrease, L decrease •  expect Black Dwarf Electron degenerate P only support up to 1.4 Msun == Chandrasekar Limit. Stars M < 5 Msun become WD

14. Stellar Evolution and the H-R Diagram: 1 solar mass • Evolution of a 1 solar mass star. • Main Stages: • Red Giant • Planetary Nebula • White Dwarf

15. Red Giant Stage: • Radius increases. • to orbit of Jupiter • Surface T decreases. • fusion of He in core  Carbon (C)

16. Planetary Nebula Model • Ejected outer envelope. • Core of star is revealed. • Hot core ionizes expanding envelope.

19. The Eskimo Nebula: • Lasts ~ 30 * 10**4 yrs. • Radius 0.25 to 2 ly.

21. View from side: Bipolar Hubble 12 HST/WFC3

22. View from side: Bipolar On right: HST/WFC3 + ALMA ALMA (yellow) shows carbon torus.

23. Red Rectangle Planetary Nebula (ESA/Hubble Image of the Week)

24. How do they get bipolar shape? ATCA Old sun-like star with jets! Jet of particles spiralling in strong B field  shape of nebula.

26. White Dwarf Stage: HST Binary system of Sirius A and Sirius B • Sirius B. • High T, low L  R very small (e.g. size of Earth). • The stellar core after the PN has dissipated. • Contracts  Degenerate Electron Gas: electrons packed as tightly as possible. • Pressure support since negative charges repulse each other. • Fades over 100s * 10**9 yrs.

27. Stellar Evolution of a 1 solar mass star: • The position of a star on the HR diagram changes as the star evolves.

29. Evolution of Stars with Mass >5 Solar Masses • Supernovae • violent explosions • outshine host galaxy •  distances for cosmology •  responsible for heavy elements in universe – 2 main types

30. Supernova Type Ia • 2 scenarios involving binary systems • a giant & white dwarf • two white dwarfs merging

31. Supernovae Type IaScenario 1. • most stars in binary star systems  giant & white dwarf. • Roche Lobe: Tear-drop shaped zone of influence of a star i.e. material within lobe “belongs” to that star. • Lagrangian point: gravitational pull of the 2 stars balances the rotation of the binary system. Material can flow through this point.

32. Supernovae Type IaScenario 1. • Tenuous material from giant falls onto WD • Limit to mass support Chandrasekhar limit ~ 1.4 Msun • as soon as mass on WD increases beyond this  core contract • T increase on surface to required for fusion • detonation all at once, blowing WD apart • no remnant

33. Supernovae Type Ia: Scenario 1 • Exceeding Chandrasekhar limit  runaway fusion totally destroying WD

34. Supernovae Type Ia: Scenario 2 • Double Degenerate: 2 white dwarfs merging • Exceeding Chandrasekhar limit  runaway fusion totally destroying WD

35. Chandra X-ray observations

36. Supernovae Type Ia • ~1.4 Msun  small range of intrinsic luminosity for peak • shape of the light curve distinguishes SNe types

37. Supernovae Type Ia • Inverse Square Brightness Law  distance to host galaxy.

38. Big Bang: The Expansion of the Universe: Observations The expansion is accelerating! SNe distance vs Doppler-shifted velocity (redshift = v/c)  Hubble Law & expansion  Dark Energy

39. 2011 Nobel prize winner! • Brian Schmidt, Saul Perlmutter, and Adam Reiss for finding that the universe’s expansion is accelerating.