1. massive star death (SNe): Chapt 21
Lecture 22 – Stellar Evolution
Star Fleet Academy
Tues: Nov 4, 18, 25
Noon
Alllen 326
Textbook on reserve at Science Library
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
ALL NOTES COPYRIGHT JAYANNE ENGLISH
The state of the affairs from the previous class is that we measure arcs on the sky.

2. 1. Star Formation – cold, dense dusty Molecular Clouds (MC):
The bits of HII regions that are going to turn into proplyds are the dense, cold clouds.
Horsehead Nebula
Bok Globules

3. 2. Star Formation (SF) in Cores in MC - Enhancements
Green Bank Telescope, mm wavelengths
Credit: S. Schnee, et al.; B. Saxton, B. Kent (NRAO/AUI/NSF)
Cores are knots in the filaments.
10 ly long dust filaments (orange) filled with pebbles
protostars, in cores, may arise in nurturing environment for planets

4. 2. Star Formation - Enhancements:
Eagle Nebula (HST)

5. 2. Star Formation - Enhancements:
dense: Density ~ 10**6 atoms/cm**3 c.f. “space” ~1 atom/cm**3 …. c.f. sealevel 10**18 particles/cm**3
cold: T ~ 10K …. -263C
Leads us back to the HR diagram
Eagle Nebula.
Evaporating Gaseous Globules (EGGs)

6. P causes dense clouds to gravitationally collapse & form stars.
3. SF - Enhancements collapse
Balloon example.
Kelvin-Helmholtz contraction.
Conservation of Angular Momentum  disk-shaped cloud.
P causes dense clouds to gravitationally collapse & form stars.
forces: gravity & external P
 self-gravity

7. 4. Star Formation proplyds with protostars in centre
Kelvin-Helmoltz contraction.

8. 5. Star Formation: Nuclear Fusion Begins – bipolar outflow
Protostar == first stage of becoming a star.
Bipolar outflows: up to 15 ly radius (i.e. length of 1 jet)
Some material from accretion disk shoots along polars at v > 10km/s … convert to hr as exercise
Starts to clear system of gas and dust
Late stage proto-star or early stage star:
T Tauri stars.
Herbig Haro Objects – bipolar outflows == jets emanating from protostars.

9. Note jet coming out of molecular cloud.
Star Formation:
Protostar buried in the molecular cloud.
Note jet coming out of molecular cloud.

10. Star Formation: Herbig Haro Jets
Radius 0.5 to 15 ly long!
Moving at 10 km/s. How many km/hr?

11. Hot young stars  blue, massive Fusion in core  Zero Age MS
6. SF: Young stars
The Pleiades .
Hot young stars  blue, massive
Fusion in core  Zero Age MS
Still surrounded by dust reflecting blue light.
group of stars with different masses.

12. Radiation & wind from O star  bubble in molecular cloud/ISM
6. SF: Young stars
The Bubble Nebula by Bernard Michaud .
Radiation & wind from O star
 bubble in molecular cloud/ISM
diameter 10 ly
M ✪ > 45 M

13. This radio & FIR image shows:
- clouds of heated dust where stars are forming (pink).
- cold neutral hydrogen gas (diffuse structure)
- the interstellar medium (ISM)

14. C A B
Which image shows gas density enhancements that are about to collapse to form proto-stars? ________
Which image shows the stage of protostar formation?______
Which image is associated with the T Tauri or bipolar outflow stage? _______
Which image shows the stage where stars have nuclear fusion occuring in their cores? _______ D

15. SF on H-R Diagram : Hayashi Track
L = 4 pi r**2 sigma T**4
100x larger than sun therefore L large
K-H contraction  T increase so move left
contraction  r decrease so L decrease
For a star like our sun to form takes up to 50 million years.
A higher mass star about 1 million years.
A lower mass star about a billion years.
Large, cool protostar in centre of proplyd nebula  in upper right.
r contracts & T increases. Kelvin-Helmholtz Contraction.
Fusion in core  on MS.

16. do not initiate nuclear fusion of H do not reside on the MS
SF on H-R Diagram: MS
Brown Dwarfs
Recall the rogue planet or small star Nibiru from the Doomsday scenarios.
Brown dwarf stars
small enough masses
do not initiate nuclear fusion of H
do not reside on the MS

17. Evolve off of MS when H in core is converted to Helium (He).
SF on H-R Diagram:
ZAMS
T~ 15*10**6K
Zero Age Main Sequence (ZAMS) at left edge of MS with advent of nuclear fusion.
Stars on MS
Evolve off of MS when H in core is converted to Helium (He).
MS is not an evolutionary track.
Star in hydrostatic equilibrium i.e.
P_outward = pull of gravity inward
Thermal P: P from radiation + heat energy
Tcore decrease  grav contraction  Tcore increase  Pout  radius
So jiggles around a bit but stays on MS

18. Name/describe to your neighbour the 6 main stages of star birth like our sun.

19. STAR

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

21. H converted to He in core H burning in shell He not burning
Leaving the MS
H converted to He in core
H burning in shell
He not burning
 no pressure P to counter gravity

23. Travels up the Red Giant Branch (i. e
Travels up the Red Giant Branch (i.e. Subgiant Branch) of the HR diagram.
Enriches ISM

26. What will happen?
Part way through the evolution of 1 solar mass – see next lecture.