1. Please press “1” to test your transmitter
The Formation of Stars
Please press “1” to test your transmitter
Fox Fur Nebula

2. The Life Cycle of Stars
Dense, dark clouds, possibly forming stars in the future
Ageing supergiant
Young stars, still in their birth nebulae
Movie: Lifes of Stars

3. Giant Molecular Clouds
Barnard 68
Infrared
Visible
Star formation ← collapse of the cores of giant molecular clouds: Dark, cold, dense clouds obscuring the light of stars behind them.
(More transparent in infrared light.)

4. How hot does the core of a cloud/star need to be to ignite nuclear fusion?
1,000 K
10,000 K.
100,000 K.
1 million K.
10 million K. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

5. Parameters of Giant Molecular Clouds
Size: r ~ 50 pc
Mass: > 100,000 Msun
Temp.: a few 0K
Dense cores:
R ~ 0.1 pc
M ~ 1 Msun
Much too cold and too low density to ignite thermonuclear processes
Clouds need to contract and heat up in order to form stars.
External trigger required to initiate the collapse of clouds to form stars.
→ Compression waves (shocks)

6. Which of the following is an example of a shock wave?
Which of the following is an example of a shock wave?
A large ocean wave.
The tides.
The loud, sudden bang of the sound of a supersonic air plane.
A Tsunami.
An Earthquake. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

7. Shocks Triggering Star Formation
Trifid Nebula
Globules = sites where stars are being born right now!

8. Sources of Shock Waves Triggering Star Formation
Previous star formation can trigger further star formation through:
a) Shocks from supernovae (explosions of massive stars):

9. Which stars live the shortest lives?
Which stars live the shortest lives?
Very massive O and B stars.
Very massive K and M stars.
Intermediate-mass A and F stars.
Low-mass O and B stars.
Low-mass K and M stars. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

10. Sources of Shock Waves Triggering Star Formation
Previous star formation can trigger further star formation through:
a) Shocks from supernovae (explosions of massive stars):
Massive (O, B) stars die young => Supernovae tend to happen near sites of recent star formation

11. What is “Ionization”? Electrons being ejected out of an atom.
What is “Ionization”?
Electrons being ejected out of an atom.
Electrons being lifted into an excited state in an atom.
Electrons annihilating on their anti-particles.
Two atomic nuclei combining to form a heavier nucleus.
A heavy atomic nucleus being split up into two lighter nuclei. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

12. Sources of Shock Waves Triggering Star Formation
Previous star formation can trigger further star formation through:
b) Ionization fronts of hot, massive O or B stars which produce a lot of UV radiation:
Massive stars die young => O and B stars only exist near sites of recent star formation

13. Sources of Shock Waves Triggering Star Formation
c) Spiral arms in galaxies like our Milky Way:
Spirals arms are probably rotating shock wave patterns.

14. Open Clusters of Stars
Large masses of Giant Molecular Clouds => Stars do not form isolated, but in large groups, called Open Clusters of Stars.
Open Cluster M7

15. Special type of Open Cluster:
O/B Associations
Special type of Open Cluster:
Very young clusters still contain very massive, very hot O and B stars, dominating the luminosity of the association and ionizing large regions of gas around them.
Orion Nebula; Trapezium Stars

16. (Bok) Globules
Compact, dense pockets of gas which may contract to form stars.
~ 10 – 1000 solar masses;
Contracting to form protostars

17. Globules
Evaporating Gaseous Globules (“EGGs”): Newly forming stars exposed by the ionizing radiation from nearby massive stars

18. Protostars Protostars = pre-birth state of stars:
Protostars = pre-birth state of stars:
Hydrogen to Helium fusion not yet ignited
Still enshrouded in opaque “cocoons” of dust => barely visible in the optical, but bright in the infrared.

19. What happens to a rotating gas cloud when it contracts?
:44
Its rate of rotation will slow down, and it takes on a disk-like shape.
Its rotation will slow down, but its shape remains approximately spherical.
Its rate of rotation will remain constant, and its shape remains approximately spherical.
Its rate of rotation will speed up, and it takes on a disk-like shape.
Its rotation will speed up, but its shape remains approximately spherical. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

20. Protostellar Disks
Conservation of angular momentum leads to the formation of protostellar disks → birth place of planets and moons

21. Protostellar Disks and Jets – Herbig Haro Objects
Disks of matter accreted onto the protostar (“accretion disks”) often lead to the formation of jets (directed outflows): Herbig Haro Objects
Herbig Haro Object HH30

22. Once thermonuclear fusion in the center of a star is ignited, the star will heat up and become more luminous. Thus, which way will it “move” in the Hertzsprung-Russell (HR) diagram?
:44
Towards the lower right.
Towards the lower left.
Towards the upper right.
Towards the upper left.
It will basically stay at the same point in the HR diagram. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

23. From Protostars to Stars
Birth Line: Star emerges from the enshrouding dust cocoon
Ignition of H → He fusion

24. Star Forming Region RCW 38