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

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

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.)

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

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)

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

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

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

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

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

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

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

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

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

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

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

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

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.

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

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

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

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

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

Star Forming Region RCW 38