Transcript Slide 1

The Formation of Stars
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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
Visible
Infrared
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.
2.
3.
4.
5.
1,000 K
10,000 K.
100,000 K.
1 million K.
10 million K.
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?
1. A large ocean wave.
2. The tides.
3. The loud, sudden bang of the sound of
a supersonic air plane.
4. A Tsunami.
5. An Earthquake.
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?
1.
2.
3.
4.
5.
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.
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”?
1.
2.
3.
4.
5.
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.
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
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:
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?
1.
2.
3.
4.
5.
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.
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?
1.
2.
3.
4.
5.
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.
From Protostars to Stars
Birth Line:
Star emerges
from the
enshrouding
dust cocoon
Ignition of
H → He
fusion
Star Forming Region RCW 38